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Baseball rules

The rules of baseball, as detailed in the Official Baseball Rules published annually by Major League Baseball (MLB), govern the professional sport and its affiliated leagues, providing a standardized framework for fair play, player safety, and consistent adjudication by umpires.^[1] These rules define the game's objective: two opposing teams of nine players each compete to score more runs than the other by striking a pitched ball with a bat and advancing runners counterclockwise around four bases—first, second, third, and home plate—before three outs are recorded in their half-inning.^[1] A standard baseball game consists of nine innings, divided into top and bottom half-innings, with the visiting team batting first in each full inning while the home team fields defensively; if tied after nine innings, extra innings are played until a winner is determined.^[1] The playing field features a 90-foot diamond-shaped infield connecting the bases, a pitcher's mound 60 feet 6 inches from home plate, and outfield fences located at a minimum of 325 feet from home plate along the foul lines and 400 feet to center field (for fields constructed after June 1, 1958), with umpires enforcing fair and foul territories to regulate play.^[1] Runs are scored only when a batter or runner legally touches all bases in order and crosses home plate, while defensive plays—such as fly outs, groundouts, strikeouts, or force plays—aim to retire batters or runners to accumulate three outs per half-inning.^[1] Central to the rules is the strike zone, an imaginary vertical rectangle over home plate from the midpoint between the batter's shoulders and the top of their uniform pants down to the hollow beneath the kneecap, where pitches judged as strikes by the home plate umpire can result in an out after three strikes or advance the count toward a full count of three balls and two strikes.^[2] Additional prohibitions include balks, illegal motions by the pitcher with runners on base that allow those runners to advance, and restrictions on defensive shifts requiring at least four infielders within the infield boundary and no more than two on either side of second base prior to the pitch.^[1] The 2025 edition incorporates minor amendments, such as penalties for improperly positioned infielders under Rule 5.02(c) and options for managerial elections during play, reflecting ongoing efforts to enhance pace, safety, and strategic balance.^[1]

Fundamentals

Objective and field layout

The objective of baseball is for each team to score more runs than its opponent over the course of the game.^[1] A run is scored when an offensive player legally advances counterclockwise around the four bases—first, second, third, and back to home plate—touching each in order without being put out.^[1] The team with the most runs at the end of nine innings (or as otherwise determined by game-ending conditions) wins.^[1] The playing field is laid out as a diamond-shaped infield forming a square with sides of 90 feet, marked by four bases positioned at the corners.^[3] Home plate, a five-sided whitened rubber slab measuring 17 inches square with beveled edges, is located at one corner and serves as the starting and ending point for runners.^[1] First, second, and third bases are 18-inch square white canvas or rubber bags, securely anchored and filled with soft material for safety; first and third bases are positioned entirely within fair territory, while second base is centered on the intersection of the diagonals.^[1] The pitcher's plate, a 24-by-6-inch whitened rubber slab, is situated 60 feet 6 inches from the rear point of home plate, atop an 18-foot-diameter mound elevated 10 inches above home plate level.^[3] Extending from the infield, the outfield forms the area between the two foul lines, which run from home plate through first and third bases to the outfield fence and are marked with white chalk or paint.^[1] Fair territory encompasses the infield, outfield, and the foul lines themselves, while foul territory includes all area outside the foul lines up to the spectator areas and fences.^[1] A batted ball landing or rolling into foul territory (unless first touched in fair territory and caught) is ruled foul, halting play and typically resulting in either a strike or an out depending on the circumstances. However, if a batted ball passes first or third base in fair territory and then rolls into foul territory, it is considered a fair ball.^[4]^[5] Major League Baseball stadiums exhibit variations in outfield boundaries and fence configurations to accommodate local architecture and historical designs, but all must comply with minimum standards outlined in the Official Baseball Rules to ensure fairness and safety.^[1] These include at least 325 feet from home plate to the foul poles (for parks built or remodeled after June 1, 1958) and 400 feet to center field, with no less than 250 feet to any obstruction in fair territory; power alleys (between foul lines and center) should measure at least 375 feet.^[3] Outfield fences must be at least 8 feet high, and the overall layout prioritizes a 95-foot radius grass line around the infield dirt for consistent playability across venues.^[1]

Equipment and uniforms

The official baseball used in Major League Baseball (MLB) games consists of a sphere with a cork, rubber, or similar core that is wound with yarn and covered with two strips of white horsehide or cowhide, tightly stitched together.^[1] It must weigh between 5 and 5.25 ounces and have a circumference of 9 to 9.25 inches, with all balls approved by the Commissioner's Office and bearing the manufacturer's mark along with MLB authentication.^[1] Intentional alteration, such as discoloration or damage, results in the ball's immediate removal from play, and the responsible player faces a 10-game suspension.^[1] Bats in MLB must be one piece of solid wood, smooth and round, without lamination or experimental designs.^[1] The maximum length is 42 inches, and the barrel diameter cannot exceed 2.61 inches, with the handle optionally treated with pine tar up to 18 inches from the end or a non-glossy finish for grip.^[1] Cupped bats are permitted if the cup depth does not exceed 1.25 inches, and no foreign substances beyond approved treatments are allowed; violations lead to the bat's removal and potential ejection.^[1] In non-professional leagues, non-wood bats made of metal or composite materials are permitted if they meet BBCOR (Batted Ball Coefficient of Restitution) certification standards to ensure performance consistency and safety. Protective equipment is mandatory to safeguard players, particularly in high-risk positions. Catchers must wear a mask with a throat protector, a padded chest protector, and shin guards that cover the entire leg from knee to ankle, along with a helmet or mask-helmet combination that fully encases the head and face without exposed metal parts.^[1] Batters and base runners are required to wear helmets with ear flaps.^[1] Fielders' gloves vary by position: first basemen's gloves have a maximum length of 13 inches and width of 8 inches with webbing not exceeding 12 inches in length from the top of the index finger pocket to the bottom of the webbing, while other infielders' and outfielders' gloves are limited to 13 inches in length, 7.75 inches in width, and 5 inches of webbing.^[1] Pitchers' gloves cannot be white, gray, or in distracting colors to maintain visibility.^[1] Player uniforms ensure uniformity and identification on the field, which measures 90 feet between bases. All team members must wear identical caps, jerseys, pants, and socks in the same color, trim, and style, with numbers at least 6 inches high on the back in a contrasting color for visibility.^[1] Undershirts must be solid-colored without patterns, and sleeves cannot be ragged or altered in a distracting manner; jewelry is permitted but must not pose a risk of injury to others.^[1] Commercial patches or logos on uniforms require prior approval to avoid excessive advertising, and non-conforming attire prevents a player from participating in the game.^[1] Umpires' equipment prioritizes safety and functionality during play. They must wear a face mask with a throat protector, a chest protector, shin guards, and either a helmet or mask-helmet combination, along with a protective cup and padded indicators for tracking balls, strikes, outs, and innings.^[1] This gear is designed for durability and visibility, ensuring umpires can officiate effectively without hindrance.^[1]

Historical development

Pre-professional era

The rules of baseball trace their origins to 18th-century bat-and-ball games in Britain and early America, particularly rounders and town ball, which featured elements like baserunning between posts or bases, batting to avoid fielders, and outs via catching or tagging (often called "plugging" or "soaking").^[6] Rounders, documented in British sources from the 1820s, involved overarm bowling, a batter running on missed pitches, and one-out-side-out for caught balls, influencing early American variants.^[6] Town ball, popular in Philadelphia and Massachusetts by the 1830s, used circular bases, allowed plugging runners with the ball, and had flexible team sizes with no fixed positions, setting the stage for baseball's informal play before codification.^[6] These games lacked standardized rules, leading to regional variations until the mid-19th century. The first formal codification came with the Knickerbocker Rules, drafted by Alexander Cartwright for the New York Knickerbocker Base Ball Club on September 23, 1845, comprising 20 guidelines that shifted from plugging to tag-outs and established key foundations like 90-foot base paths and a diamond-shaped field.^[7] Games were structured around reaching 21 runs (called "aces") rather than fixed innings, with each side taking equal "hands" (turns at bat) until that tally, and three outs ending a half-inning ("three hands out, all out").^[7]^[8] Pitching was restricted to underhand delivery from a pitcher's point 45 feet from home, with three strikes (missed swings) resulting in an out, but foul balls did not count as strikes.^[7] Outs occurred on catches "flying or on the first bound," reflecting the one-bounce rule inherited from predecessors like stoolball, and teams typically fielded around 9 players, though not explicitly fixed.^[8] In 1857, the National Association of Base Ball Players (NABBP) formed as the first organized body, initially comprising 15 New York-area clubs meeting on January 22, with official incorporation in 1858, to standardize rules for amateur play amid growing popularity.^[9] The NABBP's conventions introduced the 9-inning format, where the team with the most runs after nine equal turns won, replacing the 21-run limit, and formalized 9 players per side with defined positions.^[9] Through the 1850s and 1860s, rules evolved further: foul balls became strikes in 1858, and the one-bounce out was eliminated for fair balls in 1865 (requiring fly catches), though it lingered for fouls until 1883.^[8] The NABBP maintained an amateur ethos, banning professionals in 1859, but by the late 1860s, the amateur-professional divide emerged as paid players gained prominence, setting the stage for organized leagues.^[9] Overhand pitching, initially prohibited to preserve the game's gentility, was permitted starting in 1884, marking a shift toward more dynamic play.^[7]

Professional codification and evolution

The professional era of baseball began with the founding of the National League in 1876, which formalized the sport's rules for the first time at the major league level. This inaugural professional circuit adopted key standards that persist today, including teams of nine players each, games consisting of nine innings, and the force-out rule allowing fielders to record outs by tagging or throwing to a base before a runner arrives on ground balls. These codifications, drawn from earlier amateur conventions but now enforced in a salaried context, aimed to standardize play across clubs and elevate the game's professionalism.^[10]^[11] Early evolutions focused on balancing offensive and defensive dynamics. In 1887, the pitching distance was extended to 55 feet 6 inches to counter pitchers' dominance, though it was further adjusted to the current 60 feet 6 inches in 1893 amid ongoing debates over hitters' struggles. The foul strike rule, introduced by the National League in 1901 (and adopted by the American League in 1903), counted the first two foul balls as strikes to reduce prolonged at-bats and limit teams' expenses on replacement balls. By 1920, the spitball and other "freak" pitches were banned league-wide to promote fairer competition, with a grandfather clause allowing 17 established pitchers to continue using them until retirement.^[12]^[13]^[14]^[15] Twentieth-century changes reflected broader efforts to modernize and differentiate leagues. The American League introduced the designated hitter rule in 1973, allowing a substitute batter for the pitcher to boost offense and extend careers, though the National League resisted until universal adoption in 2022. Interleague play debuted in 1997, enabling regular-season matchups between American and National League teams to increase fan interest and revenue. Instant replay, initially limited to home run calls in 2008, expanded in 2014 to cover 13 play types, including safe/out decisions and catch/no-catch, with managers gaining challenge rights to enhance umpiring accuracy.^[16]^[17]^[18]^[19] Post-2020 updates prioritized pace of play and safety. In 2023, Major League Baseball implemented a 15-second pitch clock with bases empty (20 seconds with runners on), restrictions limiting defensive shifts to two infielders on either side of second base, and larger bases (18 inches square, up from 15) to encourage steals and reduce injuries—all tested in the minors to shorten games without altering core strategy. No major rule alterations occurred in 2024 or 2025, though minor tweaks addressed shift enforcement and replay procedures.^[20]^[21]

Game structure

Innings and game duration

A standard Major League Baseball (MLB) game consists of nine innings, with each inning divided into two halves: the top half, during which the visiting team bats, and the bottom half, during which the home team bats.^[22] Teams alternate between offense and defense in each half-inning, allowing each side an equal opportunity to score runs. An inning concludes when the defensive team records three outs against the batting team, at which point the teams switch roles for the next half-inning. The bottom half of the ninth inning (or an extra inning) ends immediately if the home team scores the winning run, or after three outs otherwise. If the home team leads after the completion of the top of the ninth or an extra inning, the bottom half is not played. This structure ensures that games progress efficiently while maintaining fairness, with outs serving as the primary mechanism for transitioning offensive and defensive turns. MLB games have no fixed time limit and are determined solely by the completion of innings, though the average duration for a nine-inning contest in the 2025 season was approximately 2 hours and 38 minutes.^[23] If the score remains tied after nine full innings, extra innings are played until one team secures a lead at the end of a complete inning or the home team scores the winning run in the bottom half; each extra half-inning begins with a runner placed on second base, who is the player in the batting order immediately preceding the batter (the one who made the last out of the previous half-inning for the opposing team).^[1] For a game to be considered official and regulation, at least five innings must be completed—or four and a half if the home team is ahead—though some league schedules permit shortened seven-inning games as exceptions. While MLB does not implement a mercy rule to terminate games early due to lopsided scores, such provisions are common in youth and minor leagues to promote player development and prevent excessive disparities.^[24] For example, Little League Baseball applies a 10-run mercy rule after four innings in tournament play, ending the game if one team leads by that margin.^[25]

Starting and ending a game

Prior to the start of a Major League Baseball game, managers from both teams exchange lineup cards with the home plate umpire during a pregame meeting, typically occurring around 30 minutes before the scheduled first pitch, where the official batting orders and fielding positions are submitted and verified.^[26]^[1] Umpires, consisting of a crew of four in MLB—led by the umpire-in-chief positioned behind the catcher at home plate, with the others covering the bases—inspect the field and equipment for readiness, ensuring compliance with ground rules.^[26]^[1] This pregame routine culminates with the national anthem, performed before every game as a ceremonial tradition, during which players, umpires, and fans stand at attention facing the flag.^[27] The game officially begins with the first pitch, called into motion when the umpire-in-chief signals "Play" after the visiting team places its first batter in the box and the home team assumes defensive positions, making the ball live until "Time" is called.^[1] The visiting team always bats first in the top of the first inning, and the starting pitcher must deliver the pitch legally, without committing a balk—defined as any deceptive or illegal motion, such as failing to complete the delivery after starting the windup, which would allow runners (if any) to advance a base if present later.^[1] The pitcher may take up to eight warm-up pitches before this initial delivery.^[1] A standard game ends after nine innings, with the team having scored the most runs declared the winner; specifically, it concludes if the home team leads following the visiting team's completion of the top of the ninth, or after the home team completes its at-bat in the bottom of the ninth if necessary.^[1] For context on the inning structure, games are divided into nine regulation innings unless shortened, but termination follows these protocols once regulation status is met (after 4.5 or 5 innings).^[1] If conditions like weather or darkness halt play before regulation, the game is suspended and resumes from the exact point of stoppage on a rescheduled date, preferably within the same series; rain delays begin with an initial assessment period, followed by a mandatory minimum 30-minute wait before resuming or calling the game.^[1]^[28] Forfeits are exceedingly rare in MLB, occurring only for severe rule violations such as a team fielding fewer than nine players, refusing to continue play after a warning, or causing excessive delays, resulting in a 9-0 victory awarded to the opposing team by the umpire-in-chief.^[1] The last MLB forfeit happened in 1995 due to fan interference disrupting play, underscoring their infrequency as a last resort for maintaining game integrity.^[29]

Offensive play

Batting mechanics

In baseball, the strike zone is defined as the space over home plate from the hollow beneath the batter's kneecap to the midpoint between the top of the shoulders and the top of the uniform pants, determined as the batter assumes their natural stance with the bat over their shoulder.^[1] A pitch entering this zone without being swung at constitutes a called strike, while any pitch outside the zone that the batter does not swing at is a ball.^[1] Three strikes result in the batter being out. A strike is a pitch over the plate that the batter swings at and misses, a called pitch in the strike zone, or a foul ball (not a bunt or caught foul tip) when the batter has fewer than two strikes. With two strikes, additional foul balls do not count as a third strike. However, if the third strike is not caught by the catcher and first base is unoccupied (or with two outs regardless of occupancy), the batter may attempt to reach first base safely.^[1] Four balls award the batter first base via a base on balls, allowing them to advance without liability to be put out. If the batter is hit by a pitched ball that does not enter the strike zone (and the batter did not swing or lean into it intentionally), the batter is awarded first base, with runners advancing one base if forced.^[1] A fair ball, which can lead to a hit, occurs when a batted ball settles on fair territory between home plate and first or third base, bounds past first or third base on or over fair ground, or touches one of the bases before going foul.^[1] Hits are classified by the farthest base the batter reaches safely: a single to first base, a double to second, a triple to third, or a home run, which occurs when the batter scores by reaching home plate safely, either by hitting the ball over the fence in fair territory (an over-the-fence home run) or by circling all the bases while the ball remains in play (an inside-the-park home run).^[1] On a home run, any runners on base also score, and the batter is not out unless they fail to touch the bases in order.^[1] Following a hit, the batter becomes a runner entitled to advance to the awarded base, with further progression governed by baserunning rules.^[1] Bunting introduces specific mechanics: a bunt is a deliberate attempt to tap the ball lightly into fair territory without swinging fully, and a foul bunt with two strikes counts as the third strike, resulting in an out unless the ball is caught in the air.^[1] In contrast, a successful sacrifice bunt, where the batter is out but advances a runner, is not charged as an official at-bat and is recorded as a sacrifice hit if it occurs with fewer than two outs.^[1] Catcher interference happens when the catcher physically hinders the batter from making contact with a pitch, entitling the batter to first base and allowing all runners to advance one base, though the offensive team may elect to decline the award and accept the result of the play if more advantageous.^[1] This penalty does not apply if the batter reaches base safely and runners advance at least as far as under the interference ruling.^[1]

Baserunning rules

Baserunners in baseball advance along the bases—first, second, third, and home—in a counterclockwise order around the diamond, touching each base legally to maintain their position and progress. A runner acquires the right to an unoccupied base by touching it before being put out and retains that right until tagged out, forced to vacate for a succeeding runner, or the ball becomes dead.^[22] If forced to return to a prior base, such as after a caught fly ball, the runner must retouch the bases in reverse order unless the ball is dead, in which case advancement or return occurs without liability to be put out.^[22] Only one runner may occupy a base at a time; if two runners touch the same base while the ball is alive, the preceding runner is entitled to it, and the following runner is out upon being tagged, except in force situations.^[22] Advancement typically occurs following a batted ball that allows runners to progress, such as a hit placing them on base. On a ground ball with occupied bases, a force play arises, requiring each runner to vacate their base and advance to the next; the defense retires the runner by touching the next base with the ball before the runner arrives, without needing to tag the runner.^[22] This force continues through all bases, including home plate when bases are loaded. Runners must touch each base in order; failing to do so intentionally or unintentionally allows the defense to appeal the miss before the next pitch or the end of the play, resulting in the runner being called out if the appeal is upheld.^[22] Runners may take a lead off their base and attempt to steal the next base by advancing during the pitcher's delivery, at their own risk of being put out, typically attempting to reach the base before the catcher's throw tags them. Successful steals credit the runner with a stolen base in official scoring.^[22]^[30] A runner is out on a tag play when a fielder in possession of the ball touches the runner with it while the runner is off their base and not attempting to return to a previously touched base. Runners may deviate up to three feet from the direct base path to avoid a tag without penalty, but exceeding this to evade the fielder results in an out. Appeal plays extend this principle to missed bases or improper returns, where the defense verbally requests an umpire's call prior to the next pitch, the bases becoming empty, or the defensive team leaving fair territory; successful appeals declare the runner out, potentially nullifying preceding runs if it constitutes the third out.^[22]^[31] A run scores when a runner legally touches home plate after advancing through all bases before three outs are recorded in the inning, provided the third out is not made by the batter-runner or a preceding runner in certain force or appeal situations. On a ground ball with bases loaded, the runner from third is forced to home, and the defense records the out by tagging the plate or the runner before they arrive. No run scores if the force out at home is the third out, even if the runner's foot touches the plate simultaneously with the tag.^[22] Obstruction occurs when a fielder, not in possession of the ball and not fielding it, impedes a runner's progress or path to a base; the umpire awards the obstructed runner at least the base they would have reached absent the obstruction, with the ball declared dead and other runners advanced accordingly. Type 1 obstruction, involving immediate hindrance during a play, results in the runner being safe and awarded bases regardless of the outcome; Type 2 allows play to continue, with awards assessed post-play if necessary. Conversely, runner interference happens when a baserunner hinders a fielder making a play on a batted ball, such as colliding with them or altering their path, resulting in the runner being called out and the ball dead, unless the interference aids a double play, in which case both the interfering runner and the batter-runner may be out.^[22]^[32]

Defensive play

Pitching regulations

In baseball, the pitcher must adhere to specific delivery mechanics to ensure fair play. The two legal pitching positions are the windup and the set position. In the windup position, the pitcher faces the batter with the pivot foot in contact with the pitcher's plate and the other foot free, delivering the pitch without interruption after any preliminary motions such as stepping backward.^[1] In the set position, used primarily with runners on base, the pitcher stands with the pivot foot on the plate, the other foot in front, holds the ball in both hands in front of the body, and comes to a complete stop before beginning the delivery, with hands together.^[1] During delivery, the pitcher must step directly toward home plate, and any failure to do so or deceptive motion constitutes a balk when runners are on base.^[1] A balk is an illegal act by the pitcher intended to deceive runners, such as failing to come to a complete stop in the set position, making a motion associated with the pitch without delivering the ball, or stepping toward a base without throwing while touching the pitcher's plate.^[1] The penalty for a balk is that the ball becomes dead, and all runners advance one base without liability to be put out; if no runners are on base, it results in a ball being awarded to the batter.^[1] Umpires enforce balk rules to prevent deliberate deception, with 13 specific actions defined as balks in Major League Baseball (MLB), including dropping the ball while touching the plate or failing to deliver after starting the windup motion.^[33] Since 2023, pitchers are limited to two disengagements (step-offs from the rubber or pickoff attempts) per plate appearance; a third unsuccessful disengagement results in a balk, unless a runner advances or is retired.^[34] Pitchers employ various pitch types, such as fastballs, curveballs, sliders, and changeups, each governed by the requirement that no foreign substances may be applied to the ball or the pitcher's person to alter its movement.^[1] MLB Rule 3.01 prohibits intentionally discoloring or damaging the ball with substances like rosin, paraffin, or emery, while Rules 6.02(c)(4) and 6.02(c)(7) ban applying or possessing foreign substances, with penalties including immediate ejection and automatic suspension.^[1] In June 2021, MLB reinforced enforcement of these rules through heightened umpire inspections, leading to multiple ejections and suspensions for violations involving "sticky stuff" like Spider Tack, aiming to maintain game integrity and reduce spin rates enhanced by such aids.^[35] MLB imposes no strict pitch count limit on pitchers, leaving decisions to managers, though typical starting pitchers throw around 100 pitches per outing to manage fatigue and injury risk, often pulling them after 85-105 pitches depending on effectiveness.^[36] To support pitcher health, guidelines recommend rest periods, such as at least one day off after 75 pitches, though these are not mandatory in professional play.^[37] Mound visits, where coaches or players confer with the pitcher, are limited to four per team per nine innings, with an additional visit allowed in the ninth if none remain, reduced from five in 2023 to accelerate pace of play; exceeding this without a pitching change results in the pitcher being removed.^[38] Warm-up pitches allow pitchers to prepare without delaying the game. At the start of each inning or upon entering as a reliever, a pitcher may throw up to eight preparatory pitches to the catcher, completed within one minute or as limited by league standards.^[1] Between innings, pitchers may also return to the bullpen for up to eight warm-up throws if it does not delay play, though the home team cannot warm up on the field before the game.^[39] In emergencies, such as injury substitutions, umpires may grant additional throws at their discretion.^[1] A quick pitch, delivered before the batter is reasonably set in the box, is illegal and aims to catch the batter off guard.^[1] Umpires judge it based on the batter's alertness, with the penalty being a balk if runners are on base—advancing them one base—or a ball if bases are empty.^[1] This rule, under 6.02(a)(5) and 6.02(b), promotes safety and fairness by preventing dangerous surprises to the batter.^[1]

Fielding positions and actions

In baseball, the defensive team deploys eight fielders excluding the pitcher: the catcher and seven others positioned across the infield and outfield to prevent the offense from scoring runs. The catcher positions directly behind home plate, equipped with protective gear including a mask, chest protector, and shin guards, to receive pitches, block wild pitches or passed balls, and prevent runners from advancing on steals or wild pitches.^[40] The infield consists of four players: the first baseman, who covers the area near first base to receive throws for outs; the second baseman, positioned to the right of second base for double plays and grounders; the shortstop, between second and third base as the primary fielder for balls hit to the left side; and the third baseman, near third base to field bunts and hard-hit balls.^[40] The outfield includes three players: the left fielder, covering the area between third base and center; the center fielder, positioned in the deepest part of the field to chase fly balls and coordinate with adjacent fielders; and the right fielder, responsible for the territory between first base and center, often facing more throws due to right-handed pull hitters.^[40] These positions allow fielders to cover the entire field effectively, with the catcher serving as the on-field strategist directing the defense.^[41] Fielders execute outs primarily by catching batted balls or throwing to bases. A fielder catches a fly ball—any batted ball that travels above the playing field in an arc—before it touches the ground or another player, resulting in an immediate out for the batter or runner, provided the catch is legal and not interfered with.^[42] For ground balls or line drives, fielders field the ball cleanly and throw it to a base to force out a runner who must vacate that base or to tag a runner physically with the ball while the runner is not on a base.^[42] Relay throws enable outfielders to assist infielders by throwing long distances to a cutoff man, typically an infielder, who then relays the ball more accurately to the intended base, minimizing errors on potential double plays or home run prevention.^[42] Under the infield fly rule, if there are runners on first and second (or bases loaded) with fewer than two outs and a fair fly ball is hit that an infielder can catch with ordinary effort, the batter is automatically out regardless of whether the ball is caught, preventing fielders from intentionally dropping it to execute a force double play.^[42] Errors occur when a fielder misplaying a batted or thrown ball allows a batter or runner to reach or advance a base safely, which they would not have done otherwise; such plays are not scored as hits but charged to the fielder, affecting batting averages and fielding statistics.^[42] In a fielder's choice, a fielder opts to put out a preceding runner at a base rather than the batter advancing on a ground ball, allowing the batter to reach first base safely unless an error intervenes; this is neither an error nor a hit, but a strategic defensive decision.^[42] Fielders have the right of way to occupy space needed to field a batted ball without hindrance from runners, and they must not be obstructed while attempting to catch a thrown ball, with violations leading to interference calls and awards to the offense.^[43] Positioning rules govern how fielders align to balance defense and fairness. Since the 2023 season, Major League Baseball has restricted defensive shifts by requiring all four infielders to have both feet on the infield dirt when the pitch is delivered, with at least two infielders positioned on each side of second base to encourage traditional infield alignment and promote action on ground balls. For violations starting in 2025, if a non-compliant infielder is the first to touch the batted ball, the batter is awarded first base and any runners advance one base.^[44] Outfielders may position freely, including shifting one to the infield as a "fifth infielder."^[45] These regulations, approved by MLB's Joint Competition Committee, aim to preserve the strategic integrity of the game while adapting to modern analytics.^[46]

Advanced rules and exceptions

Substitutions and roster management

In Major League Baseball (MLB), substitutions allow managers to replace players during a game to optimize performance, with no limit on the number of substitutions permitted, provided they adhere to roster constraints. A substitution can occur at any time the ball is dead, such as between innings or after a play concludes, and the manager must immediately notify the umpire of the change. The substitute enters the game in the replaced player's batting order position and assumes their defensive responsibilities if applicable; once a player is removed, they cannot re-enter the game under MLB rules.^[47]^[48] Pitching changes follow specific protocols to maintain game flow, including the three-batter minimum rule implemented in 2020 and still in effect for 2025. A relief pitcher must face at least three batters or pitch until the end of the half-inning before being removed, unless the pitcher sustains an injury or illness that prevents continuation, in which case an exception applies. This rule aims to reduce mid-inning pitching changes and shorten game times, with the new pitcher required to complete their minimum unless the inning ends earlier due to outs. Starting pitchers are exempt from this minimum in their initial appearance but must adhere to it if returning later in the game.^[49] The designated hitter (DH) rule, universal across both leagues since its adoption in the National League in 2022, permits a team to designate one player to bat in place of the pitcher without affecting the pitcher's defensive role. The DH bats in a fixed position in the lineup—typically resulting in a 10-player batting order—and cannot enter the field defensively without forfeiting the DH designation, at which point the pitcher must bat in their stead. If the pitcher is substituted, the DH continues to hit for the new pitcher unless further changes occur. MLB teams maintain an active roster of 26 players for regular-season games, expanded to 28 from September 1 through the end of the season, with a maximum of 14 pitchers on the roster during that period. This roster determines the pool of available substitutes, and all players on the active roster may participate, though position players are generally restricted from pitching except when their team is trailing by eight or more runs, leading by ten or more runs in the ninth inning or later, or during any extra inning—to prevent unnecessary risks. The batting order, consisting of 9 or 10 players depending on DH usage, remains fixed throughout the game unless an injury forces a substitution, in which case the replacement assumes the injured player's spot without altering the sequence.^[50]

Special situations and ties

In baseball, extra innings occur when the score is tied after the completion of nine innings, with play continuing until one team secures a lead that cannot be overcome in the inning's remainder. According to Major League Baseball (MLB) rules, the game concludes when the visiting team has scored more runs than the home team at the end of a completed inning, or when the home team scores the winning run in an uncompleted inning.^[22] To expedite resolutions and reduce game length in regular-season contests, MLB implemented a rule in 2020—made permanent in 2023—placing an automatic runner on second base at the start of each extra half-inning beginning after the ninth. This designated runner is the player who made the last out in the previous inning, or the player who would have been in that position if substituted. The rule does not apply to postseason games, including the World Series, where extra innings proceed without the placed runner.^[51] Ties are rare in professional baseball and do not occur in MLB regular-season or postseason play, as games proceed to extra innings until a winner is determined. A tie game is defined as a regulation contest called with both teams having the same number of runs, but if called while tied, it becomes a suspended game to resume later from the point of interruption. In exhibitions, international competitions under World Baseball Softball Confederation (WBSC) rules, or certain minor leagues, ties may be permitted after a set number of innings or time limit to avoid prolonged play. For instance, some Single-A and Rookie leagues call ties after extra innings if conditions warrant, though MLB prioritizes completion.^[22]^[52] Replay review, introduced in 2008 for home runs and expanded in 2014, allows managers to challenge certain on-field calls to ensure accuracy using video evidence reviewed at MLB's Replay Operations Center in New York. Each team receives one manager challenge per regular-season game, with a second challenge granted only if the initial one is successful; postseason and All-Star games start with two challenges, retaining successful ones. Reviewable plays include home runs (fair/foul, fan interference), catches (complete or not), force outs, tags, passing runners, and collisions at home plate, but not judgment calls like balls and strikes or routine outs. From the eighth inning onward, the crew chief may initiate reviews on non-challenged plays without limit. In 2025, the average review time remains under two minutes, with approximately 50% of challenges overturned based on prior seasons' data. Crew chief-initiated reviews focus on close or controversial plays to maintain game integrity.^[53]^[54] Weather interruptions, such as rain or darkness, fall under the umpire-in-chief's authority, who may suspend play when conditions make further action impossible, requiring at least a 30-minute delay before calling the game. A game becomes official—and thus final if called—after five full innings (or 4.5 if the home team leads), with the score at interruption standing unless suspended. If weather halts a regulation game while tied, it is treated as suspended and resumed from that point on a subsequent date, often the next scheduled day in a doubleheader. Doubleheaders, required for suspended games or makeups, feature two contests on the same day, with the first starting no later than 1 p.m. local time if weather permits, and each counting separately for standings. Umpires consult league officials and weather experts, prioritizing player safety, with "weather takes precedence" in decisions.^[22]^[55] Umpires possess the authority to eject players, managers, coaches, or trainers for objecting to decisions, using unsportsmanlike conduct or language, or engaging in physical altercations, requiring the ejected individual to immediately leave the field and remain out of sight in the clubhouse or stands. Ejections for arguing balls and strikes or fair/foul calls must follow specific protocols, but fighting or assaulting umpires triggers immediate removal and reporting to the commissioner within four hours. While general ejections do not carry automatic suspensions, the commissioner imposes penalties, typically a one-game suspension for arguing and longer terms (up to 10 games or more) for flagrant violations like physical contact or inciting crowds. For example, ejections involving foreign substances on the ball result in automatic 10-game suspensions. Fines accompany suspensions and must be paid within five days, or the offender faces debarment.^[22]^[56]

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