Definition. A curveball is a breaking pitch that has more movement than just about any other pitch. It is thrown slower and with more overall break than a slider, and it is used to keep hitters off-balance. Most professional pitchers possess either a curveball or a slider -- and some possess both breaking pitches.
Curveball grip Place your middle finger along the bottom seam of the baseball. When this pitch is thrown, your thumb should rotate upward and your middle finger should snap downward. The arm action is a little abbreviated at the end.