A relief pitcher generally has two good pitches--a fastball and some other pitch such as a slider, screwball, or changeup. Because of their limited pitch selection, relief pitchers can rarely pitch to batters more than once during a game. Therefore, they often only pitch one or two innings.

Up until 1970, relief pitchers were generally starting pitchers who no longer were able to throw for several innings. However, after that time, relief pitchers became a specialized position.