Curveball

In baseball and softball, the curveball is a type of pitch thrown with a characteristic grip and hand movement that imparts forward spin to the ball, causing it to dive as it approaches the plate. Varieties of curveball include the 12–6 curveball, power curveball, and the knuckle curve. Its close relatives are the slider and the slurve. The "curve" of the ball varies from pitcher to pitcher.

The expression "to throw a curveball" essentially translates to introducing a significant deviation to a preceding concept.