In baseball, an appeal play occurs when a member of the defensive team calls the attention of an umpire to an infraction which he would otherwise ignore.

Live ball appeals

A runner shall be called out, after a successful live ball appeal, if he:

• failed to tag up on a batted ball caught in-flight,
• failed to touch a previous base the last time he passed it, or
• failed to touch all previous bases in order

To properly execute a live ball appeal, a fielder must, with a live ball, tag the runner or base in question and communicate to the umpire what the infraction was and which runner committed the infraction. Any such appeal must occur before the next pitch or attempted play, aside from other appeals. No live ball appeal may occur on a runner who misses a non_force base and immediately attempts to correct his mistake; this runner must be tagged in order to be put out.

Other appeals

A member of the defensive team may appeal to the umpire when a batter bats out of turn. The umpire then enforces the penalty for batting out of turn, if any.

When a batter appears to have swung at a pitch, but the umpire_in_chief calls it a ball, a member of the defensive team (usually the pitcher or catcher) may appeal for information from a base umpire on whether the batter swung. The field umpire then signals whether the batter swung, and such a judgment must, by rule, prevail. This is the only circumstance in the rules of baseball where an umpire is obligated to "ask for help" from his partner on the field. This procedure was introduced because it is commonplace for an umpire-in-chief to be unable to see some swings.

In U.S. high school games or other games governed by NFHS rules, the defense may execute any of the live ball appeals above during a dead ball by simply communicating the infraction to the umpire. Thus it is never necessary to attempt a live ball appeal; it is always safer for the defense to ask for time to make the ball dead, and then make any requests to the umpire.