Middle reliever

In baseball, middle relief pitchers (or "middle relievers") are relief pitchers who commonly pitch in the fifth, sixth, or seventh innings. In the National League, a middle reliever often comes in after the starting pitcher has been pulled for a pinch hitter. A middle reliever is usually replaced in the eighth or ninth innings by a left-handed specialist, setup pitcher or closers; middle relief pitchers may work these innings as well, especially if the game is not close.

...
Wikipedia