This is a baseball term defined as substitute player for the current hitter. The National League is the only division within Major League Baseball that uses the pinch hitter. The American League uses a designated hitter. A pinch hitter is a permanent substitute, and must remain in the game once put in. The player the substitute is replacing is not allowed to come back in. This is often used to prevent a pitcher from hitting, as pitchers are typically the worst hitter on the team and get tired after pitching 6-7 innings. It is also used to put a better hitter up at the plate if the team is in need of runs.
One of the more common uses of the pinch hitter is to bring in a relief pitcher to replace a batter who comes up much later in the lineup, while the pinch hitter to takes the place of the starting pitcher in the batting order. This helps to improve the batting strength of the lineup while simultaneously getting a new pitcher on the mound. It is important to note that the pinch hitter will also have to play the field, if they are not substituted out again. However, they do not have to play the exact position of the player they replaced, as long as every position is covered. The current record holder for greatest number of pinch hits is Lenny Harris, a utility hitter who last played for the Florida Marlins in 2005.