In baseball, a pinch hitter is a batter in place of another batter. Batters can be substituted at any time while there is not an active play. The manager may use any player who has not entered the game. Unlike basketball, American football, or ice hockey, baseball does not have a "free substitution rule". The player replaced by the pinch hitter is never allowed back into that game. The pinch hitter takes the spot in the batting order of the player that he replaces.
The player chosen to be a pinch hitter is often a backup infielder or outfielder. Catchers are not usually pinch hitters because most teams only have two catchers. Pitchers are also not used very often as pinch hitters because they are not very good hitters.
The American League of Major League Baseball, the Pacific League in Japan, the KBO League in Korea, and other leagues use the designated hitter rule. The designated hitter bats for the pitcher but does not play defense.