A relief pitcher or reliever is a baseball or softball pitcher comes in and plays the game after the starting pitcher is removed because of injury, ineffectiveness and/or fatigue. Relievers are also divided informally into closers, middle relief pitchers, left-handed specialists and set-up pitchers.
Fastballs and some other pitch(s) such as a slider, screwball, changeup or any other breaking ball pitch are usually what relievers throw. Usually since relievers have a limited pitch selection, batters tend to adjust quickly, which effects relievers in repeat at-bats. They often only pitch one or two innings because of this, but sometimes relievers pitch longer than a few innings, and sometimes until the end of the game, especially for closers.
Generally a long time ago, relievers were former starting pitchers who no longer had the energy or endurance to pitch for several or many innings. Relief pitching became a specialized position starting from the 1930s and 1960s,.
Some of the best known reliever pitches include Keith Foulke, Eric Gagné, and Mariano Rivera. Four relievers are currently in the Baseball Hall of Fame – Hoyt Wilhelm, Rollie Fingers, Dennis Eckersley, and Bruce Sutter.