Baseball (MLB) Rules Explained

Section 1: Introduction

1.1 Overview and History

Baseball is a bat-and-ball sport played between two teams of nine players each. The sport is governed at the professional level in the United States and Canada by Major League Baseball (MLB), whose Official Baseball Rules (OBR) constitute the authoritative ruleset for professional play. The edition referenced throughout this document is the 2025 Official Baseball Rules, as published by MLB and administered for the 2025 and 2026 seasons. MLB coordinates with the World Baseball Softball Confederation (WBSC) for international play, though this document focuses on MLB rules.

The objective of baseball, as stated in OBR Rule 1.01, is: "Baseball is a game between two teams of nine players each, under direction of a manager, played on an enclosed field in accordance with these rules, under jurisdiction of one or more umpires." Each team alternates between batting (offense) and fielding (defense). The team that scores the most runs by the conclusion of the game wins.

1.2 Objective of the Game

Per OBR Rule 1.05, the objective of each team is to win by scoring more runs than the opponent. A run is scored when a baserunner legally advances around all bases — first, second, third, and home — in order. The team with the most runs at the end of nine innings is declared the winner. If the score is tied after nine innings, additional innings are played until one team has more runs at the end of a complete inning (or when the home team scores the winning run in the bottom half of an inning).

1.3 Structure of the Game

A standard professional game consists of nine innings. Each inning is divided into two halves: the top half, in which the visiting team bats, and the bottom half, in which the home team bats. Each half-inning continues until the defensive team records three outs. As specified in OBR Rule 5.01, the home team takes the field first and the visiting team bats first in each inning.

Beginning in 2023 and continuing into the 2026 season, MLB has implemented several pace-of-play rules, including the pitch clock, shift restrictions, and larger bases, all of which are detailed in the relevant sections of this document.

Section 2: Equipment

2.1 The Baseball (OBR Rule 3.01)

Per OBR Rule 3.01, the baseball must be a sphere formed by yarn wound around a small core of cork, rubber, or similar material, covered with two stripes of white horsehide or cowhide, tightly stitched together. Official specifications:

Weight: Not less than 5 nor more than 5¼ ounces avoirdupois (141.75–148.83 grams)
Circumference: Not less than 9 nor more than 9¼ inches (22.86–23.49 cm)
The home club shall have available for use during a game at least three dozen regulation baseballs.
Each ball shall be presented to the umpire-in-chief at least 2 hours before game time.

2.2 The Bat (OBR Rule 3.02)

Per OBR Rule 3.02(a), the bat shall be a smooth, round stick not more than 2¾ inches (6.985 cm) in diameter at the thickest part and not more than 42 inches (106.68 cm) in length. The bat shall be one piece of solid wood, or formed from a block of wood consisting of two or more pieces of wood bonded together with an adhesive in a manner approved by the Commissioner.

Cupped bats (Rule 3.02(b)): An indentation in the end of the bat up to 1 inch (2.54 cm) in depth is permitted, so long as it is no wider than 2 inches (5.08 cm) and no less than 1 inch (2.54 cm) in diameter.
Pine tar restriction (Rule 3.02(c)): The bat handle may be covered with any material or substance to improve the player's grip, but such material or substance shall not extend more than 18 inches (45.72 cm) from the bottom of the handle. Violation results in the bat being removed from play; no out or other penalty is imposed on the batter.
Bats that are discolored, laminated, or experimentally treated in a manner not approved by the Commissioner are prohibited.

2.3 Gloves and Mitts (OBR Rule 3.05–3.07)

All fielders, with the exception of the first baseman and catcher, may use a glove or mitt of any weight. OBR Rule 3.05 specifies size limits:

Fielder's glove: Not more than 12 inches (30.48 cm) measured from the tip of any finger to the bottom of the glove, and not more than 7¾ inches (19.685 cm) wide across the palm.
First baseman's mitt (Rule 3.06): Not more than 12 inches (30.48 cm) from top to bottom and not more than 8 inches (20.32 cm) wide across the face.
Catcher's mitt (Rule 3.07): Not more than 38 inches (96.52 cm) in circumference and not more than 15½ inches (39.37 cm) in height.
Pitcher's glove: The pitcher's glove, including the lacing and any webbing, shall be a uniform solid color. The color white or gray is not permitted for the pitcher's glove (Rule 3.05(c)).

2.4 Helmets and Protective Equipment (OBR Rule 3.09)

Per OBR Rule 3.09, batters must wear a protective helmet while at bat, while running the bases, and while in the on-deck circle. Helmets must carry the official approval mark of the Commissioner and must have at least one ear flap (facing the pitcher). Catchers must wear a catcher's helmet and mask, chest protector, and shin guards during all games. As of the 2023 season, MLB mandates two-ear-flap helmets for all position players in certain situations, and continues to phase in enhanced concussion-protection requirements.

2.5 Uniforms (OBR Rule 3.03)

Per OBR Rule 3.03(a), all players on a team shall wear uniforms identical in color, trim, and style. Shoes with pointed spikes similar to track or golf shoes are prohibited (Rule 3.03(b)). No player may wear a uniform bearing the number of a player on the opposing team's active roster.

Section 3: Playing Area

3.1 The Playing Field (OBR Rule 2.01)

Per OBR Rule 2.01, the playing field is laid out per the Official Baseball Rules diagram. The infield is a 90-foot (27.432 m) square, with bases at each corner. The bases are numbered counterclockwise: first base (right), second base (center), third base (left), and home plate. The pitcher's plate (rubber) is located at the center of the diamond.

3.2 The Bases (OBR Rule 2.02)

Per OBR Rule 2.02:

Home plate: A 17-inch (43.18 cm) square of whitened rubber, set in the ground so the front edge is even with the rear corner of the batter's box. The sides extending back must be beveled.
First, second, and third base: Must be 15 inches (38.10 cm) square, between 3 and 5 inches (7.62–12.70 cm) thick, and filled with soft material. They must be securely attached to the ground.
Larger bases (effective 2023): First, second, and third base were increased from 15 inches to 18 inches (45.72 cm) square beginning with the 2023 season, as part of MLB's pace-of-play and safety initiatives. Home plate dimensions remain unchanged.
The distance from home plate to second base and from first base to third base is 127 feet, 3⅜ inches (38.795 m).

3.3 The Pitcher's Mound (OBR Rule 2.04)

Per OBR Rule 2.04, the pitcher's plate (rubber) shall be a rectangular slab of whitened rubber, 24 inches (60.96 cm) by 6 inches (15.24 cm). It shall be set in the ground so the front edge is 60 feet, 6 inches (18.44 m) from the rear point of home plate. The top of the pitcher's mound shall be 10 inches (25.4 cm) higher than home plate. The slope of the mound begins 6 inches (15.24 cm) in front of the pitcher's plate and descends at a rate of 1 inch per foot (8.33 cm per 30.48 cm) for a distance of at least 6 feet (182.88 cm).

3.4 The Batter's Box, Catcher's Box, and Coaches' Boxes (OBR Rule 2.05–2.07)

Batter's box (Rule 2.05): 4 feet (121.92 cm) wide by 6 feet (182.88 cm) long, located on either side of home plate.
Catcher's box (Rule 2.06): 8 feet (243.84 cm) in length and 43 inches (109.22 cm) wide.
Coaches' boxes (Rule 2.07): Located adjacent to first and third base, each 8 feet (243.84 cm) by 15 feet (457.20 cm).
On-deck circles: Two circles, 5 feet (152.40 cm) in diameter, located near the dugouts for the next batter to warm up.

3.5 Fair and Foul Territory (OBR Rule 2.01, Definitions)

Per the OBR Definitions of Terms, "Fair Territory" is that part of the playing field within and including the first base and third base lines from home base to the bottom of the playing field fence, and as further determined by the foul lines. "Foul Territory" is that part of the playing field outside the first base and third base lines extended to the fence and perpendicularly upward. The foul poles at the outfield fence, which are at least 325 feet (99.06 m) from home plate along the foul lines in stadiums built after June 1, 1958, mark the boundary between fair and foul territory in the outfield.

3.6 The Dugout

Each team has a dugout, one on each side of the playing field. Only players in uniform, managers, coaches, trainers, and batboys may occupy the dugout during a game (OBR Rule 4.05). Dugouts must be enclosed and below field level in professional stadiums.

Section 4: Players & Officials

4.1 Teams and Rosters (OBR Rule 4.01–4.03)

Per OBR Rule 4.01, a regulation game is played between two teams of nine players each. Each team's manager must deliver to the umpire-in-chief and the opposing manager a batting order containing each starting player's name and position at least 5 minutes before the scheduled game time for day games and 10 minutes for night games. Once a player's name is submitted in the batting order, they are considered in the game for the purposes of lineup integrity.

MLB rosters during the regular season consist of a 26-player active roster (expanded to 28 from September 1 through the end of the regular season) and a 40-man roster. Substitutions must be reported to an umpire, who shall announce or cause to be announced the substitution to the official scorer and the public address announcer (OBR Rule 5.10(b)).

4.2 Substitutions (OBR Rule 5.10)

Per OBR Rule 5.10(a), the manager shall immediately notify the umpire-in-chief when a substitution is made. A substitute player, once entered in the game, cannot be removed and re-entered; a player removed from the game is finished for that game. The designated hitter (DH), introduced in the American League in 1973 and adopted universally in MLB starting with the 2022 season, is covered under OBR Rule 5.11.

4.3 The Designated Hitter (OBR Rule 5.11)

Per OBR Rule 5.11, a hitter may be designated for any pitcher, but not be a fielder. Selection of a designated hitter is optional and must be announced before the game. If the DH is removed for a pinch hitter or pinch runner, that player becomes the new DH. If the DH takes a fielding position, the team loses the DH for the rest of the game and the pitcher must bat in the order vacated by the player replaced by the pitcher.

4.4 The Umpires (OBR Rule 8.01–8.04)

Per OBR Rule 8.01, the umpire-in-chief (home plate umpire) shall have general authority to enforce all rules, call balls and strikes, make all rulings on the batter, and have authority to remove players, managers, or coaches for violations. A full crew for MLB games consists of four umpires (home plate, first base, second base, third base). In postseason play, six umpires are used (adding left field and right field umpires).

Rule 8.02(a): Umpires shall not reverse a decision unless they determine that the rule was misapplied.
Replay Review: Under MLB's Replay Review system (in effect since 2014, expanded in subsequent seasons), managers may challenge reviewable calls. Each team receives one challenge per game; if the challenge is successful, the team retains the challenge. Beginning in 2020, the umpire crew chief may also initiate a review on certain calls. Non-reviewable calls include balls and strikes, check swings, and interference/obstruction in certain circumstances.
Rule 8.04: Umpires are authorized to remove any player, manager, or coach who uses objectionable language or acts in a manner deemed to be against the best interests of the game.

4.5 The Manager and Coaches (OBR Rule 4.05–4.06)

Per OBR Rule 4.05, the manager is responsible for the conduct of the team and must be in uniform. Each team is entitled to a manager and up to six coaches (as per current MLB rules). Coaches must remain in the coaches' boxes at all times while a game is in progress, unless coaching a runner or receiving permission from the umpire to confer with a player.

Section 5: Rules of Play

5.1 Starting the Game (OBR Rule 5.01)

Per OBR Rule 5.01, the home team takes the field and the visiting team sends its first batter to the plate to start the game. Before the game starts, the umpire-in-chief calls "Play" to begin. The pitcher must pitch to the first batter within the time limits of the pitch clock (see Rule 5.07(c)).

5.2 The Pitch Clock (OBR Rule 5.07(c)) — Effective 2023

Beginning with the 2023 season, MLB implemented a mandatory pitch clock under OBR Rule 5.07(c):

The pitcher must begin the pitching motion within 15 seconds of receiving the ball from the catcher (or when the pitcher is otherwise ready) when no runners are on base.
The pitcher must begin the pitching motion within 20 seconds when runners are on base.
The batter must be in the batter's box and "alert to the pitcher" with at least 8 seconds remaining on the clock.
Violation by the pitcher: An automatic ball is added to the count.
Violation by the batter: An automatic strike is added to the count.
A pitcher may disengage (step off the rubber) up to two times per plate appearance without penalty; a third disengagement that does not result in an out or advance restores the limit to two on the next disengagement.

5.3 Pitching (OBR Rule 5.07)

Per OBR Rule 5.07(a), the pitcher must take the pitching position by standing on the pitcher's plate in one of two legal positions:

The Windup Position: The pitcher faces the batter, with the pivot foot in contact with the pitcher's plate and the other foot free.
The Set Position: The pitcher stands facing the batter with the pivot foot in contact with the pitcher's plate. The pitching hand and glove hand must be brought to a stop ("set") before delivering the pitch.

Per Rule 5.07(b), the pitch is considered delivered when the pitcher's arm passes the hip in the forward swing. Illegal pitches (e.g., a pitch delivered from an illegal position, a quick pitch, or a pitch while in an illegal position) result in a ball being awarded to the batter, or, with runners on base, a balk.

Per Rule 5.07(d) — Pitcher Limits (Three-Batter Minimum): A pitcher (other than a starting pitcher) must face a minimum of three batters, or the remainder of the inning (whichever comes first), unless the pitcher sustains an injury or illness that, in the umpire-in-chief's judgment, incapacitates the pitcher from further play. This rule was adopted effective the 2020 season.

5.4 Batting (OBR Rule 5.04)

Per OBR Rule 5.04(a), batters shall bat in the order their names appear in the batting order. Each batter's turn at bat commences when they step into the batter's box and concludes when they are put out, becomes a baserunner, or is substituted for by a pinch hitter. A batter is out if:

Three strikes are called against them (strikeout), per Rule 5.09(a)(1).
A fair or foul fly ball (not a foul tip) is caught by a fielder before it touches the ground, per Rule 5.09(a)(1).
An infield fly is declared under the Infield Fly Rule (Rule 5.09(a)(12)).
The batter hits into a force play or is tagged out.

Per OBR Rule 5.04(b)(4), the batter may leave the batter's box once per plate appearance without penalty, provided the batter does not delay the game. Violation of time limits (see pitch clock rules) results in a called strike.

5.5 Baserunning (OBR Rule 5.05–5.09)

Per OBR Rule 5.05(a), a batter becomes a baserunner when:

A fair ball is hit that is not caught on the fly.
The catcher fails to catch the third strike and first base is unoccupied, or there are two outs (dropped third strike, Rule 5.05(a)(2)).
Four balls (a walk) are called by the umpire, per Rule 5.05(b)(1).
The batter is hit by a pitched ball and attempts to avoid the pitch, per Rule 5.05(b)(2).
A fair ball, in the umpire's judgment, is deflected by a fielder and leaves the playing field, per Rule 5.05(b)(3).

Runners must touch bases in order (first, second, third, home) and may be forced out or tagged out. A baserunner is out if they run more than 3 feet (91.44 cm) outside a direct line between bases to avoid a tag (Rule 5.09(b)(1)), unless doing so is to avoid interfering with a fielder fielding a batted ball.

5.6 The Infield Fly Rule (OBR Rule 5.09(a)(12))

Per OBR Rule 5.09(a)(12), an infield fly is a fair fly ball (not a line drive or bunt) that can be caught by an infielder with ordinary effort, when first and second bases, or first, second, and third bases are occupied before two are out. The batter is declared out by the umpire immediately; runners may advance at their own risk after the ball is caught or they may remain on their bases.

5.7 Shift Restrictions (OBR Rule 5.02(c)) — Effective 2023

Per OBR Rule 5.02(c), beginning in 2023, infield positioning restrictions require that at the time of each pitch, all four infielders must be positioned within the outer boundary of the infield (i.e., on the infield dirt or grass of the infield area), with two infielders on each side of second base. No infielder may position themselves in the outfield grass prior to the pitch. Violation results in the offensive team's manager choosing to accept the result of the play or having an automatic ball added to the count.

5.8 Recording Outs (OBR Rule 5.09)

Per OBR Rule 5.09, the defensive team records outs in the following ways (among others):

A fly ball caught before touching the ground (out on appeal or force not required).
A runner tagged with the ball while not in contact with a base (tag out).
A runner is forced to advance and the fielder with the ball touches the base before the runner (force out).
A batter-runner is tagged or the ball beats the runner to first base.
A runner passes another runner who has not been put out (Rule 5.09(b)(9)).
A runner fails to retouch a base after a fly ball is caught and an appeal is properly made (Rule 5.09(c)).

Section 6: Scoring

6.1 How Runs Are Scored (OBR Rule 5.08)

Per OBR Rule 5.08(a), one run shall be scored each time a runner legally advances to and touches home base before three men are put out to end the inning. Exception: A run is not scored if the runner advances to home during a play in which the third out is made by the batter-runner before reaching first base, or by any runner being forced out, or by a preceding runner who is declared out on appeal.

6.2 The Home Run

A home run occurs when a batter hits a fair ball over the outfield fence in flight. Per OBR Definitions (Home Run), the batter is awarded home base and all runners on base also score. A fair ball that bounces over or through the outfield fence is ruled a ground-rule double, not a home run. An "inside-the-park home run" occurs when the batter and all preceding runners reach home on a batted ball that remains in play throughout.

6.3 Earned and Unearned Runs (OBR Rule 9.16)

Per OBR Rule 9.16, an earned run is any run for which the pitcher is held accountable — i.e., a run that scores without the benefit of an error or passed ball. An unearned run is charged to the pitcher only if it would not have scored but for a fielding error or passed ball. The official scorer is responsible for determining which runs are earned and which are unearned.

6.4 Extra Innings and Tiebreakers

If the score is tied at the end of nine innings, additional innings are played until a winner is determined. Per OBR Rule 7.01, starting in the 2020 season (COVID-shortened season) and adopted permanently for the 2023 season onward, MLB uses the "Manfred Rule" (runner on second base to start each extra inning): each half-inning of extra innings begins with the player who made the last out of the preceding inning placed on second base. This rule is confirmed in MLB's current collective bargaining agreement and rule amendments for the 2022 CBA period.

6.5 Official Scorer (OBR Rule 9.01–9.02)

Per OBR Rule 9.01, the Official Scorer shall observe the game from a position in the press box and shall have sole authority to make all decisions involving judgment, such as whether a batter's advance to first base is the result of a hit or an error. All decisions by the Official Scorer are final unless reversed by the Commissioner. The Official Scorer shall report all scoring decisions to the official statisticians of the league.

6.6 Regulation Games (OBR Rule 7.01–7.04)

Per OBR Rule 7.01, a regulation game consists of nine innings, unless extended because of a tie score, or shortened because the home team needs none of its half of the ninth inning or only a fraction of it, or because of weather or other causes. A game is considered "official" (a regulation game) after five innings (or 4½ innings if the home team is ahead), per OBR Rule 7.01(a). If a game is called before becoming a regulation game, it is a "no game" and must be replayed from the beginning.

Per OBR Rule 7.02, if a game is called after it has become a regulation game and the score is tied, it is a suspended game and must be resumed from the point of suspension. If a game is called after it has become a regulation game and one team is ahead, the game is complete and the score at the time of the call is the final score.

Section 7: Violations & Penalties

7.1 Balk (OBR Rule 6.02(a))

Per OBR Rule 6.02(a), it is a balk when a pitcher, while in contact with the pitcher's plate, commits any of the following acts (among others):

Makes any motion associated with a pitch without actually delivering the pitch.
Fakes a throw to first or third base while in contact with the pitcher's rubber.
Fails to step directly toward a base before throwing to that base while on the rubber.
Pitches while not facing the batter.
Makes a quick pitch (an intentionally rushed delivery before the batter is set).
Drops the ball while on the rubber.
Fails to come to a full and complete stop in the set position before delivering the pitch.
Delivers a pitch while the catcher is not in the catcher's box (intentional walk, Rule 6.02(a)(12)).

Penalty: Each runner is awarded one base. The batter receives no benefit unless forced to advance.

7.2 Illegal Pitch (OBR Rule 6.02(b))

Per OBR Rule 6.02(b), an illegal pitch is a pitch delivered while the pitcher's pivot foot is not in contact with the pitcher's plate (when no runners are on base). The penalty is a ball added to the count. If a batter reaches base safely on an illegal pitch, or if all runners advance one base on the play, the illegal pitch is disregarded.

7.3 Interference (OBR Rule 6.01)

Per OBR Rule 6.01, interference is an act by the team at bat that impedes, hinders, or confuses any fielder attempting to make a play. Types of interference include:

Batter interference (Rule 6.01(a)): Batter interferes with the catcher's throw by stepping out of the batter's box, or by any other act. Penalty: The batter is out; runners return to their bases.
Runner interference (Rule 6.01(a)(5)): A runner intentionally contacts a batted or thrown ball or a fielder. Penalty: The runner is out; other runners may or may not be allowed to advance.
Spectator interference (Rule 6.01(e)): A spectator reaches out of the stands and touches a live ball. Penalty: The umpire shall impose penalties sufficient to nullify the act of interference. The ball is dead.
Catcher's interference (Rule 6.01(g)): The catcher hinders or impedes the batter. The batter is awarded first base; runners advance if forced.

7.4 Obstruction (OBR Rule 6.01(h))

Per OBR Rule 6.01(h), obstruction is the act of a fielder who, while not in possession of the ball and not in the act of fielding the ball, impedes the progress of any runner. Two types are defined:

Type A (Rule 6.01(h)(1)): Obstruction occurs while a play is being made on the obstructed runner. The ball is dead; the obstructed runner is awarded at least the base they were attempting to reach.
Type B (Rule 6.01(h)(2)): Obstruction occurs while no play is being made on the obstructed runner. Play continues; the obstructed runner is protected from being put out.

7.5 Foreign Substances and Doctored Balls (OBR Rule 6.02(c))

Per OBR Rule 6.02(c), a pitcher shall not apply a foreign substance of any kind to the ball, deface the ball in any manner, deliver a shine ball, spit ball, mud ball, or emery ball, or intentionally damage or roughen the surface of the ball. Umpires are empowered to inspect the pitcher and catcher for foreign substances at any time. As of June 2021, MLB implemented enhanced enforcement of this rule with mandatory checks:

Penalty (Rule 6.02(c)(7)): The pitcher is ejected from the game and suspended for ten games.
The ball is removed from play.

7.6 The Infield Fly Rule Violation

When the infield fly rule is in effect and the umpire declares "Infield Fly," the batter is automatically out regardless of whether the ball is caught. If a fielder intentionally drops an infield fly, the ball remains live and in play (OBR Rule 5.09(a)(12)). Runners may advance at their own risk.

7.7 Appeal Plays (OBR Rule 5.09(c))

Per OBR Rule 5.09(c), an appeal is when a fielder claims a runner failed to touch a base, failed to retouch a base after a fly ball was caught, or missed home plate. An appeal must be made before the next pitch, intentional base on balls, or the infielders leave the infield after the third out. To appeal, the pitcher, catcher, or any other fielder must tag the runner or the missed base while the ball is in play. The umpire will then rule on whether the appeal is valid.

7.8 Pine Tar Incident and Bat Violations (OBR Rule 3.02(c))

If a bat with pine tar or other material extending more than 18 inches (45.72 cm) from the knob is discovered after a home run is hit, the home run stands and the bat is removed from play (see Pine Tar Game precedent, reaffirmed in 2023 rule clarification). The batter is not called out for having an illegal bat unless the bat is discovered during the at-bat per Rule 6.03(a)(5).

7.9 Ejections and Suspensions (OBR Rule 8.04)

Per OBR Rule 8.04, umpires are authorized to eject any player, manager, or coach who commits objectionable acts, including but not limited to: arguing balls and strikes, using offensive language, inciting spectators, or refusing to comply with umpire rulings. Ejected individuals must leave the playing field immediately and are subject to further discipline from the Commissioner's Office including fines and suspensions.

Section 8: Safety Considerations

8.1 Protective Equipment Requirements

MLB mandates specific protective equipment for all players in active game situations under OBR Rule 3.09 and supplementary league rules:

Batting helmets: All batters, on-deck batters, and baserunners must wear an approved helmet. Helmets must meet National Operating Committee on Standards for Athletic Equipment (NOCSAE) certification standards. Two-ear-flap helmets are standard for all minor league players and have been phased in at the MLB level.
Catcher's equipment: Catchers must wear a helmet with face mask (or a one-piece helmet/mask), chest protector, and shin guards in all game situations. Beginning in 2024, MLB recommends catchers wear a concussion-prevention cervical spine protector, though it is not yet mandatory.
Pitchers: As of 2023, padded pitcher's caps with enhanced protection are available as optional equipment. MLB has undertaken ongoing review of mandatory pitcher protective headwear following line-drive incidents.

8.2 Collision Rules at Home Plate (OBR Rule 6.01(i))

Per OBR Rule 6.01(i), implemented in 2014 and finalized in 2015:

A runner attempting to score may not deviate from the direct path to home plate in order to initiate contact with the catcher.
The catcher may not block the runner's path to home plate unless the catcher is in possession of the ball. A catcher without the ball who blocks the plate is deemed to be obstructing the runner.
Penalty (runner violation): The runner is called out; the ball is dead and no other runners may advance.
Penalty (catcher violation): The runner is called safe; the ball is dead and other runners advance per obstruction rules.
The rule is subject to Replay Review.

8.3 Sliding Rules and Takeout Slides (OBR Rule 6.01(j))

Per OBR Rule 6.01(j), adopted in 2016 following the Chase Utley slide incident in the 2015 postseason:

A runner attempting to break up a double play must make a bona fide attempt to reach and stay on the base.
The runner must reach the base before or at the time they make contact with the fielder.
The runner must not change their path or attempt to initiate contact with the fielder for the purpose of preventing a throw.
Penalty: Both the runner and batter-runner are declared out. This rule is a reviewable play under the Replay Review system.

8.4 Hit Batters and Batter Safety (OBR Rule 5.05(b)(2))

Per OBR Rule 5.05(b)(2), a batter hit by a pitched ball is awarded first base, provided they attempted to avoid the ball and the pitch was not in the strike zone. The umpire has authority to issue warnings to both benches if a hit batter or other conduct suggests intentional throwing at batters. Following a warning, any pitcher who hits a batter with a pitched ball is subject to ejection (OBR Rule 6.02(d)(1)).

8.5 Mound Visits and Pitcher Health

Per OBR Rule 5.10(l), each team is limited to five mound visits per nine-inning game without removing the pitcher (one additional visit is permitted for each extra inning). A visit that includes the pitcher's removal is not counted against the limit. This rule, implemented in 2018, also contributes to player welfare by reducing fatigue-inducing warm-up delays. When a pitcher is removed for injury reasons, the umpire may grant additional time for the replacement pitcher to warm up without counting against the new pitcher's allotted warm-up pitches.

8.6 Suspended Games and Weather Delays

Per OBR Rule 7.02 and supplementary MLB policy, all games shall be stopped if conditions make play unsafe, including lightning, severe weather, or field conditions that present a hazard. The umpire-in-chief has final authority to suspend play. Games suspended due to weather after becoming regulation games (five full innings, or 4½ innings with the home team leading) shall be resumed from the point of suspension, not replayed from the beginning, per current MLB policy.

8.7 Concussion Protocol

MLB's concussion protocol, established jointly by MLB and the MLB Players Association (MLBPA) under the CBA, requires that any player who exhibits signs, symptoms, or behaviors consistent with a concussion be immediately removed from the game. The player is placed on the Injured List (IL) and must be evaluated and cleared by a physician before returning to play. An emergency Medical Services team is required to be on-site or immediately accessible at every MLB venue during all game activity.

8.8 Foreign Substance Checks and Pitcher Welfare

During enhanced foreign substance enforcement (effective June 2021), umpires conduct checks between half-innings. These checks are conducted in a respectful manner, and the Commissioner's Office has stated that the primary purpose is fair play, not penalization of a player's health or physical needs. Pitchers may use approved rosin (from the rosin bag on the mound) to improve grip at any time during a game, per OBR Rule 6.02(c)(7).