Baseball (MLB) — Official Rules

Baseball is a game between two (2) teams of nine (9) players each, under the direction of a manager, played on an enclosed field in accordance with these rules, under the jurisdiction of one or more umpires. The offensive team bats and tries to score runs; the defensive team fields and tries to make outs and prevent runs.

The objective of each team is to win by scoring more runs than the opponent. The winner of the game shall be the team that has scored, in accordance with these rules, the greater number of runs at the conclusion of a regulation game. There is no clock: a game is decided by innings, not time.

The infield shall be a 90-foot (27.43 m) square. Home base, first, second and third base form the four corners. The two foul lines extend from home plate through first and third base to the outfield fence and define fair and foul territory. It is desirable that the line from home base through the pitcher's plate to second base run east-northeast, and that the minimum distance from home plate to the nearest fence be 250 feet down the foul lines (recommended 320 ft or more) and 400 feet to centre field on newer parks.

Home base shall be a five-sided slab of whitened rubber, 17 inches wide. First, second and third base are bags 18 inches (45.7 cm) square and 3 to 5 inches thick (the bases were enlarged from 15 to 18 inches in 2023 to improve safety and base-running). The bases shall be securely attached to the ground.

The pitcher's plate shall be a rectangular slab of whitened rubber 24 inches by 6 inches, set 10 inches (25.4 cm) above the level of home plate and 60 feet 6 inches (18.44 m) from the back point of home plate. The mound slopes downward from a point 6 inches in front of the plate, dropping 1 inch per foot for 6 feet toward home plate.

The ball shall be a sphere formed by yarn wound around a small core of cork, rubber or similar material, covered with two strips of white horsehide or cowhide tightly stitched together. It shall weigh not less than 5 nor more than 5.25 ounces (142-149 g) and measure not less than 9 nor more than 9.25 inches (22.9-23.5 cm) in circumference.

The bat shall be a smooth, round stick not more than 2.61 inches in diameter at the thickest part and not more than 42 inches (106.7 cm) in length. It shall be one piece of solid wood (an experimental hollowed cupped end up to 1.25 inches deep is permitted). No laminated, coloured or experimental bat may be used in a championship game unless approved.

All players on a team shall wear uniforms identical in colour, trim and style, with individual identifying numbers at least 6 inches high on the back. A batter and any base runner must wear a protective helmet; the catcher must wear a catcher's mitt, mask and protective gear. Fielders other than the catcher use a fielder's glove that conforms to the dimensional limits of Rule 3.06-3.07.

A regulation game consists of nine (9) innings. Each inning has two halves: the visiting team bats in the top half, the home team bats in the bottom half. A half-inning ends when the fielding team records three (3) outs. The home team does not bat in the bottom of the ninth if it is already ahead.

A game is regulation (official) once the trailing team has batted at least 5 innings (or 4.5 if the home team leads). If a game is called (e.g., for weather) after it becomes regulation, the score stands. If called before it is regulation, it is a suspended game to be resumed, or replayed, per league rules. A tie game that is called shall be resumed from the point of stoppage.

A game cannot end in a tie. If the score is tied after nine innings, play continues with full extra innings until one team leads at the end of a complete inning, or the home team scores to win in the bottom half. In the regular season (permanent since 2023), each half-inning of extra innings begins with an automatic runner placed on second base (the player who made the last out of the previous inning, or a pinch-runner); this runner is charged as unearned. The automatic-runner rule does not apply in the postseason.

A pitch timer governs pace of play. The pitcher must begin the motion to deliver within 15 seconds with the bases empty and 18 seconds with runners on base (reduced from 20 seconds in 2024). The batter must be in the box and alert to the pitcher by the 8-second mark. A pitcher is limited to two disengagements (pickoffs/step-offs) per plate appearance; a third that does not retire a runner is a balk. Penalties: an automatic ball for a pitcher violation, an automatic strike for a batter violation, and 30 seconds are allowed between batters.

A strike is a pitch that passes through the strike zone, or is swung at and missed, or is fouled with fewer than two strikes. A ball is a pitch outside the strike zone at which the batter does not swing. The traditional strike zone is the area over home plate between the midpoint of the batter's shoulders and the top of the uniform pants (top) and the hollow beneath the kneecap (bottom), as the batter is prepared to swing.

Each batter faces a count of balls and strikes. Four (4) balls entitle the batter to a base on balls (a walk), advancing to first base. Three (3) strikes put the batter out (a strikeout); a third strike that is not caught by the catcher may allow the batter to attempt first base if it is open or there are two outs. A foul ball counts as a strike unless the batter already has two strikes (a foul with two strikes does not add a strike, except a foul bunt, which is a strikeout).

A balk is an illegal motion by the pitcher with one or more runners on base (e.g., feinting to first, not coming to a complete stop in the set position); the penalty is that all runners advance one base. A wild pitch or passed ball allows runners to advance on a ball that gets past the catcher. A batter hit by a pitch outside the strike zone, while attempting to avoid it, is awarded first base.

A pitcher who enters the game must pitch to a minimum of three (3) consecutive batters, including the batter then at bat, until those batters are put out or reach base, or until the offensive half-inning ends. Exceptions are made only for injury or illness. The rule limits frequent pitching changes and shortens game length.

Each team submits a batting order of nine players before the game; players must bat in that order throughout. After the ninth batter, the order returns to the first. A batter who bats out of turn may be called out on a proper appeal. A substitute takes the place in the batting order of the player replaced.

When the batter hits a fair ball, he becomes a runner. A single reaches first, a double second, a triple third, and a home run allows the batter and all runners to circle the bases and score. A fair ball hit over the outfield fence in flight is a home run; a fair ball that bounces over or is deflected over the fence is a ground-rule double, advancing all runners two bases.

One run is scored each time a runner legally advances to and touches first, second, third and home base before three are out to end the inning. A run does not count if the third out is made: (a) by the batter-runner before reaching first; (b) by any runner being forced out; or (c) by a preceding runner failing to touch a base on appeal. The team's total runs determine the winner.

A runner may attempt to advance to the next base while the pitcher delivers (a stolen base). If the defense tags the runner before he reaches the base, he is caught stealing and is out. With the larger 18-inch bases and the two-disengagement limit on pitchers (since 2023), stolen-base attempts and success rates have increased.

A batter or runner is out when, among other ways: he is struck out (three strikes); a fielder catches a fair or foul ball on the fly (a flyout/lineout); the batter-runner is thrown out at first before reaching the base (a groundout); a runner is tagged with the ball off base; or a runner is forced out because the batter became a runner and the defense touches the next base first. Three outs retire the side and end the half-inning.

A double play is a play in which two offensive players are put out as a continuous action (e.g., a force at second followed by a throw to first). A triple play records all three outs of the half-inning on a single continuous play. Both are credited only when the action is unbroken.

An error is charged by the official scorer to a fielder whose misplay (a fumble, muff or wild throw) prolongs the time at bat of a batter, prolongs the life of a runner, or permits a runner to advance, when ordinary effort would have resulted in an out. Runs that score as a result of an error are generally unearned for the pitcher.

A manager may substitute any player at any time the ball is dead. A substituted player may not re-enter the game (no re-entry). A pinch hitter bats in place of a scheduled batter, and a pinch runner replaces a runner on base; the substitute then occupies that spot in the batting order. A new pitcher must meet the three-batter minimum (Rule 5.04).

Each club carries a 26-player active roster (28 in September). The number of pitchers is limited to 13 on the 26-player roster. A position player may pitch only in extra innings, when his team is trailing by 8 or more runs, or when his team is leading by 10 or more runs in the ninth inning (unless the player is a designated two-way player). These limits curb the use of position-player pitching and roster manipulation.

Under the universal designated hitter (DH) adopted permanently in 2022, each club may name a designated hitter who bats for the pitcher throughout the game without otherwise affecting the defensive lineup. Under the two-way ('Ohtani') rule, a player who starts as both pitcher and DH may continue to hit even after he is removed as pitcher.

When the pitch is released, the defense must have a minimum of four infielders, with at least two infielders completely on either side of second base, and all four must have both feet on the infield dirt. Players may not switch sides of the infield for a given batter. The penalty for a violation is an automatic ball (or, at the offense's option, the result of the play). This 2023 rule effectively bans extreme infield shifts.

The game is administered by umpires, typically four in the regular season (home plate, first, second and third base) and more in the postseason. The plate umpire calls balls and strikes and rules on the batter; base umpires rule on plays at the bases. Umpires have full authority to enforce the rules, eject players or managers, and forfeit a game.

A manager may challenge most reviewable calls (e.g., safe/out at a base, fair/foul in the outfield, home-run boundary, catch/no-catch). Each manager begins with one challenge (two in some postseason rounds) and retains it after a successful overturn. From the 8th inning on, the crew chief may initiate a review of a reviewable call. Ball/strike calls are not reviewable by manager challenge; they fall under the ABS system (Chapter 11).

For the full 2026 season, MLB adopts the Automated Ball-Strike (ABS) Challenge System. The home-plate umpire still calls every pitch, but a call may be challenged to the automated system. Each team starts with two (2) challenges per game. A challenge may be initiated only by the batter, pitcher or catcher, immediately after the call, by tapping the helmet or cap — no help from the dugout or other players is allowed. A team keeps the challenge if the call is overturned and loses one if the call stands.

For ABS purposes, the strike zone is a two-dimensional rectangle over the midpoint of home plate, 17 inches wide (the width of the plate), with the top set at 53.5% of the batter's height and the bottom at 27% of the batter's height — a fixed, per-player zone. The ball is judged by its position as it crosses the plate's centre. In extra innings, a team that has used both challenges is granted one additional challenge for each extra inning played.