A strategic baseball maneuver in which the team manager makes two defensive substitutions at once. Typically done in the late innings of a ballgame, when a pitcher (who is poor at the plate) is scheduled to bat in the next half-inning. By inserting a relief pitcher and a substitute fielder, the non-pitching defensive substitute can take the previous pitchers place in the batting order, in hopes of generating more offense when your team is next at bat.
A hallmark of the National League, where the pitcher is in the batting order and hits for himself, as opposed to the American League, where the Designated Hitter, or DH, bats for the pitcher.