A knuckleball (or knuckler for short) is a baseball pitch with an erratic, unpreictable motion. The pitch is thrown so as to minimize the spin of the ball in flight. This causes vortices over the stitched seams of the baseball during its trajectory, which in turn can cause the pitch to change direction -- and even corkscrew -- in mid-flight. This makes the pitch difficult for batters to hit, but also difficult for pitchers to control. The challenge also extends to the catcher, who must at least attempt to catch the pitch, and the umpire, who must determine whether the pitch was a strike or ball.