Rule Book

A baseball game is divided into 9 innings. Each inningA unit of play with a top half (visitors bat) and bottom half (home bats); a regulation game has 9. has two halves: in the top half the visiting team bats, in the bottom half the home team bats. A team gets 3 outs per half-inningA unit of play with a top half (visitors bat) and bottom half (home bats); a regulation game has 9.. A regulation game is 27 outs per side. The team with the most runs after 9 innings wins; tied games go to extra innings.

The pitcherThe fielder on the mound who throws each pitch. Position number 1. throws to the catcherCrouches behind home plate, calls pitches, and throws out base stealers. Position 2.; the batter tries to hitA ball put in play that lets the batter reach base safely without an error. the ball into fair territory. The strike zoneThe vertical column over home plate from the batter's knees to mid-chest. Pitches inside it are strikes; outside are balls. is the column over home plate from the batter's knees to mid-chest. Three strikes is a strikeout (outThree outs end a half-inning. Recorded by strikeout, fly out, ground out, force out, or tag.). Four balls is a walk (free pass to first base). Modern starting pitchers throw 4-pitch arsenals: fastball, slider, curveball, and changeup are most common.

Nine fielders defend: pitcherThe fielder on the mound who throws each pitch. Position number 1., catcherCrouches behind home plate, calls pitches, and throws out base stealers. Position 2., four infielders (1B, 2B, SS, 3B), and three outfielders (LF, CF, RF). Outs are recorded by strikeout, fly outThree outs end a half-inning. Recorded by strikeout, fly out, ground out, force out, or tag. (caught in the air), force outThree outs end a half-inning. Recorded by strikeout, fly out, ground out, force out, or tag. (touching the base before the runner), or tag outThree outs end a half-inning. Recorded by strikeout, fly out, ground out, force out, or tag. (touching the runner with the ball). The infield fly rule prevents intentional drops from starting cheap double plays. Baserunners advance on hits, walks, errors, or stolen bases.

A runScored when a runner safely touches all four bases (1st, 2nd, 3rd, home). scores when a runner safely touches all four bases (1st, 2nd, 3rd, home). The line score shows runs per inningA unit of play with a top half (visitors bat) and bottom half (home bats); a regulation game has 9. plus totals: R (runs), H (hits), E (errors). Key batting stats: AVG (batting average), OPS (on-base + slugging). Key pitching stats: ERAEarned Run Average. Earned runs allowed per 9 innings. Lower is better; 3.00 is excellent. (earned runScored when a runner safely touches all four bases (1st, 2nd, 3rd, home). average), WHIPWalks + Hits per Inning Pitched. Measures baserunners allowed. 1.10 is elite. (walks + hits per inningA unit of play with a top half (visitors bat) and bottom half (home bats); a regulation game has 9.). Earned runs exclude runs that scored because of an errorA misplay by a fielder that lets a batter reach or a runner advance. Reflected as 'E' on the line score..

Managers can challenge most close calls (safe/outThree outs end a half-inning. Recorded by strikeout, fly out, ground out, force out, or tag., fair/foul, home runA hit (usually over the fence in fair territory) that scores the batter and any runners. boundaries, catch/no-catch). New for 2026: the ABS Challenge System lets the batter, pitcherThe fielder on the mound who throws each pitch. Position number 1., or catcherCrouches behind home plate, calls pitches, and throws out base stealers. Position 2. challenge ball-strike calls — each team gets 2 challenges per game (only successful ones are retained). Replay decisions come from MLB's central replay center in New York, typically resolved in under 90 seconds.

Active rules for the 2026 season: pitch clock — 15 seconds with the bases empty, 18 seconds with runners (since 2023). Three-batter minimum for relievers. Larger 18-inch bases (since 2023). Shift restrictions — two infielders on each side of second base, both feet on the dirt. Ghost runner placed on second base to start each extra inningA unit of play with a top half (visitors bat) and bottom half (home bats); a regulation game has 9. in the regular season (not in the postseason). Position players cannot pitch unless leading by 10+, trailing by 8+, or in extra innings. 26-man active roster with a 13-pitcherThe fielder on the mound who throws each pitch. Position number 1. max. New for 2026: the ABS challenge system rolls outThree outs end a half-inning. Recorded by strikeout, fly out, ground out, force out, or tag. league-wide.