A triple play occurs when the defending team records three outs on a single defensive play.
Triple plays are rare for several reasons. First off, they can occur only when the batting team has at least two men on base with nobody out. Then, in those cases, the batting team typically has to make a baserunning blunder to aid the defending team. The most common form of a triple play begins with a hard line drive at an infielder. In this instance, runners sometimes have already left their bases -- either to steal, as part of a hit and run or simply because they didn't get a good read on where the ball was headed. The defense will then throw to both bases, getting both runners out.
Still, there is no common method for a triple play, like there is with a ground-ball double play. There have been ground-ball triple plays, typically with a slow runner batting. There have also been situations where multiple runners get caught in rundowns. Additionally, triple plays have resulted from confusion at an umpire's call.
One of the rarest occurrences in baseball is the unassisted triple play, where a single fielder turns a triple play without ever giving up the baseball. There are no defensive assists on the play, and thus it is unassisted. Every unassisted triple play in history (through the 2016 season) has followed a pattern, where the three outs are recorded by: 1. An infielder catching a line drive, and 2. that infielder tagging a runner and stepping on second base (in no particular order).
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