A changeup is a type of pitch in baseball. Other names include change-of-pace, Bugs Bunny change-up, the dreaded equalizer, and simply change. The changeup is sometimes called an off-speed pitch, although that term can also be used simply to mean any pitch that is slower than a fastball. In addition, before at least the second half of the twentieth century, the term slow-ball was used to denote pitches not a fastball or breaking ball, which almost always meant a type of changeup. Therefore, the terms slow-ball and changeup could be used interchangeably.

The changeup is thrown with the same arm action as a fastball, but at a lower velocity due to the pitcher holding the ball in a special grip. Leo Mazzone states: "When a pitcher throws his best fastball, he puts more in it; the changeup is such that one throws something other than his best fastball. By having this mindset, the pitch will have less velocity on it in addition to the change in grips. This difference from what is expected by the arm action and the velocity can confuse the batter into swinging the bat far too early and thus receiving a strike, or not swinging at all. Should a batter be fooled on the timing of the pitch and still make contact, it will cause a foul ball or the ball being put into play weakly, usually resulting in an out. In addition to the unexpectedly slow velocity, the changeup can also possess a significant amount of movement, which can bewilder the batter even further. The very best changeups utilize both deception and movement."