High Quality Content by WIKIPEDIA articles! A relief pitcher or reliever is a baseball or softball pitcher who enters the game after the starting pitcher is removed due to injury, ineffectiveness, fatigue, ejection, or for other strategic reasons, such as being substituted by a pinch hitter. Relief pitchers are further divided informally into closers, set-up relief pitchers, middle relief pitchers, left-handed specialists, long relievers, and mop-up relief pitchers.