In 1959, Lyman Briggs (1874–1963) demonstrated that a ball can curve up to 17.5 inches (44.45 centimeters) over the 60 feet 6 inches (18.4 meters) it travels between a pitcher and a batter, ending the debate of whether curve balls actually curved or if the apparent change in course was merely an optical illusion. Briggs studied the effect of spin and speed on the trajectory and established the relationship between amount of curvature and the spin of the ball.

A rapidly spinning baseball experiences two lift forces that cause it to curve in flight. One is the Magnus force named after H.G. Magnus (1802–1870), the German physicist who discovered it, and the other is the wake deflection force. The Magnus force causes the curve ball to move sideways because the pressure forces on the ball’s sides do not balance each other. The stitches on a baseball cause the pressure on one side of the ball to be less than on its opposite side. This forces the ball to move faster on one side than the other and forces the ball to “curve.” The wake deflection force also causes the ball to curve to one side. It occurs because the air flowing around the ball in the direction of its rotation remains attached to the ball longer and the ball’s wake is deflected.