knuckleball.

About knuckleball

A knuckleball or knuckler is a baseball pitch thrown to minimize the spin of the ball in flight, causing an erratic, unpredictable motion. While it is often incorrectly stated that the air flow over a seam of the ball causes the ball to change from laminar to turbulent flow, it has been recently shown that turbulence transition would cause the ball to move in the opposite direction as it does. Instead, the seam causes the boundary layer to detach, altering the pressure distribution and the force on the ball. At the same time, this detachment alters the shear stress on the ball, causing the seam positions to move. This makes it difficult for batters to hit but also difficult for pitchers to control and catchers to catch. Umpires are challenged as well, as the ball's irregular motion through the air makes it harder to call balls and strikes. A pitcher who throws knuckleballs is known as a knuckleballer.