The rulebook, in plain English.

A balk is an illegal act by the pitcher with runners on base — an attempt to deceive the runners, or one of thirteen enumerated violations like failing to come to a full stop from the set position. The ball is dead immediately and every runner advances one base.

A quick pitch is a delivery made before the batter is reasonably set in the box, thrown to catch him off guard. With runners on it is a balk; with the bases empty it is an automatic ball.

Pitchers may not apply any foreign substance to the ball, deface it, or have anything sticky on their hands, glove, or uniform. Umpires inspect pitchers between innings, and a violation means immediate ejection — plus a suspension under MLB's discipline policy.

Pitchers must begin their delivery before the timer expires — 15 seconds with the bases empty, 20 with runners on. Batters must be in the box and alert to the pitcher with at least 8 seconds left. Violations are automatic: a ball on the pitcher, a strike on the batter.

The pitcher may disengage from the rubber — a pickoff throw or a step-off — only twice per plate appearance while runners are on. A third disengagement has to produce an out, or it's a balk and the runners advance.

At the moment the pitch is released, the defense must have four infielders with both feet on the infield dirt, two on each side of second base. The full-shift era is over — no parking three infielders on the pull side.

Every half-inning from the tenth on starts with a runner on second base — the player who made the last out of the previous inning (or a substitute). He is real in every way that matters for the score: runs he scores count fully for the team and the game total.

A catch requires secure possession of the ball in the hand or glove plus a voluntary release — a fielder who clamps the ball but drops it only when he hits the ground has usually not caught it. Control through contact is the whole test.

A batted ball is judged by where it is when it is touched or when it stops — not where the fielder is standing. The foul lines and foul poles are fair territory, and a ball that comes to rest or is first touched beyond first or third base is judged by where it is at that moment.

With runners on first and second (or the bases loaded) and fewer than two outs, a fair fly ball an infielder can catch with ordinary effort is an automatic out — the umpire declares 'infield fly' and the batter is out whether or not the ball is caught. The rule exists so a fielder cannot drop an easy popup on purpose to force a cheap double play.

When a fair batted ball bounces over the fence, wedges in the wall, or is deflected out of play, the batter and every runner are awarded exactly two bases from the time of the pitch — even if a runner could easily have scored.

When a fielder throws the ball into the stands or dugout, every runner gets two bases. The subtle part is two bases from where: from the time of the pitch if the throw was the first play by an infielder, otherwise from where the runners were when the throw was released.

If the catcher does not catch strike three cleanly, the batter can run to first — but only when first base is unoccupied or there are two outs. Otherwise he is simply out, which stops defenses from dropping the ball on purpose to start a cheap double play.

A batter touched by a pitch takes first base — as long as he was in a legal position and made some attempt to get out of the way. If the pitch was in the strike zone or he swung, it is a strike instead, and no base is awarded.

On a caught fly ball, a runner must retouch his base before advancing. The clock starts at the fielder's first touch of the ball — not the completion of the catch — so runners can leave the moment the ball hits the glove.

Some outs never happen unless the defense asks for them. Missed bases, leaving early on a fly, and failing to touch home are not called by the umpire on his own — the defense must appeal before the next pitch or play.

A runner struck by a fair batted ball in fair territory before it has passed an infielder is out, and the ball is dead. If the ball already got through or deflected off an infielder and no other fielder had a play, the runner is fine and the ball stays live.

A runner is out if he goes more than three feet from a direct line to the base to avoid a tag. The catch: the baseline only exists once a fielder tries to tag him — until then, his path is his own.

A runner who passes a teammate ahead of him on the bases is out, full stop. The ball stays live, and it does not matter whether the pass was intentional — losing track of the runner in front is one of baseball's self-inflicted outs.

A run scores if the runner touches home before the third out is made — unless that third out is a force play, the batter-runner failing to reach first, or a preceding runner put out on appeal. In those three cases the run never counts, no matter the timing.

Breaking up a double play now requires a bona fide slide: hit the ground before the base, stay within reach of it, and make no attempt to change path or roll into the fielder. Violate it and both the runner and the batter are out.

Runners may not deviate from their path to lower the shoulder or push through the catcher, and catchers without the ball may not block the runner's lane to the plate. Both halves are enforced: a dirty slide into the catcher means out; an illegal block means safe.

Interference is the offense illegally impeding the defense — a runner contacting a fielded ball, a batter stepping in front of the catcher's throw, a coach grabbing a runner. The penalty is almost always an out, a dead ball, and runners sent back.

When the catcher's glove touches the bat during the swing, the batter is awarded first base and the catcher is charged with an error. If the offense does better than first base anyway — say the batter homers — the manager can take the result of the play instead.

Obstruction is the mirror of interference: a fielder without the ball — and not in the act of fielding it — impedes a runner. The umpire's job is to nullify the act, awarding whatever bases the runner would have reached had it not happened.

When a spectator reaches onto the field of play and touches a live ball or a player, the ball is dead and the umpires place everyone where they judge the play was headed. Reaching over the field is interference; catching a ball that has crossed into the stands is not.

Two narrow cases: the plate umpire hinders the catcher's throw on a steal or pickoff attempt, or a fair batted ball strikes an umpire before passing an infielder. The first sends the runners back; the second is a dead ball with the batter awarded first.

A regulation game is nine innings — or eight and a half if the home team leads. If weather ends things early, the game becomes official once five innings are complete (four and a half if the home team is ahead). Anything shorter is suspended and resumed later, not declared over.

A suspended game is not over and not erased — it is paused. Play resumes from the exact point of suspension on a later date, same score and situation, with the lineup carried forward as closely as the rules allow.

Managers get one challenge per game — kept if the call is overturned — and the crew chief can initiate reviews late in games and on boundary home runs any time. Only defined play types are reviewable; judgment calls like balls and strikes are untouchable.

Famous loophole: the rulebook never defines a swing. Whether the batter 'struck at' the ball is pure umpire judgment, appealable to the base umpire — first base umpire for right-handed hitters, third base for lefties — and never reviewable by replay.