Pinch-hitter

In baseball, a pinch hitter is a substitute batter. Batters can be substituted at any time while the ball is dead (not in active play); the manager may use any player who has not yet entered the game as a substitute. Unlike basketball, American football, or ice hockey, baseball does not have a "free substitution rule" and thus the replaced player in baseball is never allowed back into that game. The pinch hitter assumes the spot in the batting order of the player whom he replaces.

The player chosen to be a pinch hitter is often a backup infielder or outfielder. In the major leagues, catchers are less likely to be called upon because most teams have only two catchers, while pitchers are almost never used as pinch-hitters, because they tend to be worse hitters than other players on the team. The pinch hitter may not re-enter the game after being replaced with another player.

The American League of Major League Baseball, the Pacific League in Japan, the KBO League in Korea, and various other leagues use the designated hitter rule, such that pitchers seldom bat. This removes one possible situation where a pinch hitter may be desired.

Pinch hitters are often used to replace a starting player when the pinch hitter is thought to have a better chance of reaching base or helping other runners to score.

In the National League of Major League Baseball, the Central League in Japan, and various other minor leagues, pinch hitters are often substituted for the pitcher in the middle or late innings of a game. This is because pitchers are often poor hitters and get tired after six to seven innings of pitching. Besides, when the manager already plans to replace the pitcher in the next inning, the major downside of using a pinch hitter, namely that the player being replaced cannot re-enter the game, is taken away.

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Wikipedia