knuckleball

thumb|National Baseball Hall of Fame and Museum|Hall of Fame knuckleballer [[Hoyt Wilhelm shows how he placed his fingers before a pitch.]]

A knuckleball or knuckler is a baseball pitch thrown to minimize the spin of the ball in flight, causing an erratic, unpredictable motion. The air flow over a seam of the ball causes the ball to change from laminar to turbulent flow. This change adds a deflecting force to the baseball, making 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.