It turns out that the path of a curveball really does curve as it flies through the air, making it unpredictable and hard to hit. Exploratorium staff physicist Paul Doherty explains where the curveball gets its curve.

What causes a curveball to curve?

Curveballs curve — or break downward — because of the spin imparted by the pitcher as he flings it toward home plate. The way Briggs explained it, the rotation of the seams creates a "whirlpool" of air around the ball and causes the pressure to be lower on one side.

Which way does a curveball curve?

The side of the ball with the most pressure will push the ball towards the side of lower air pressure, causing the ball to curve! This example explains the path of a curveball that's thrown with a clockwise spin. If a ball is thrown with a counter-clockwise spin, it will curve towards the left.