A change-up (aka change, change of pace, slow ball) is a pitch that is thrown with the same motion as a fastball but much less speed. The speed contrast between fastball and change-up makes both pitches more effective. A batter who expects a fastball and gets a well-thrown change-up will swing early and either miss the ball entirely, pull it foul, or hit it very weakly. A batter who expects a change-up and gets a fastball will swing very late, and will also either miss it, hit it foul, or hit it very weakly.
Early pitchers threw change-ups by simply throwing the ball slower than normal, an effect that they could enhance by dragging their foot with their stride. This was only partially effective, though, because batters could see the change in arm speed. The modern change-up works by having the pitcher change his grip on the baseball. The different grip cuts the speed of the pitch without changing arm speed, but it can make the change-up difficult to control.
There are many different ways of throwing a change-up, some of which are specific enough that they're considered to be independent pitches:
- A straight change is thrown much like a fastball, but the ball is held against the ball and first joint of the index and middle fingers rather than the last joint and fingertips. This cuts the effective whip action of the pitcher's arm and hence the speed of the ball.
- A palm ball is held in the palm of the hand. In some variants, it's held with all of the fingers, while in others it's gripped between the thumb and pinky.
- A forkball is gripped between the index and middle finger, which are forced very wide apart. The forkball picks up a tumbling rotation that gives it a sharper downward movement than a straight change, and it is often considered a separate pitch.
- A circle change is gripped by the last three fingers while the thumb and index finger are held in a circle, much like an "OK" sign or "F" in American Sign Language. A circle change has a sideways break much like a screwball, and has largely replaced the screwball because it's much easier on the pitcher's arm.
- David Adler et al.: "Here are baseball's nastiest changeups", mlb.com, April 1, 2020.