The curveball is a type of pitch in baseball thrown with a grip and hand motion that induces extra rotation on the ball causing it to "break," to fly in a more exaggerated curve than would be expected. The pitch is slower than a fastball, and this difference in velocity also tends to disrupt the hitter's timing. Good curveballs often seem to drop sharply with a sharp rotation as they reach the plate, making the batter swing above it. The rotation on a curveball should be in the same direction as that of a fastball so the hitter cannot easily distinguish between the pitches; as such, the drop on such a ball should be 12 to 6 on a watch (although many pitchers are successful with a curve ball that breaks down and away from the batter, rather than straight down).

Ideally, a curveball will have the most break when it reaches the plate, thus making it hardest to hit. A curveball that fails to break soon enough is called a "hanging curve" and is much easier to hit. Also, batters anticipating a curveball may try to move forward (closer to the pitcher) in the batter's box to hit the curve before it breaks.

A screwball is similar to a curveball, but thrown from the back of the hand in order to impart opposite rotation and opposite movement. The knuckle curve is a variant of the curveball.

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• List of pitches
• Magnus effect
• Riseball