In Major League history, the term knuckle curve refers to two entirely different pitches.

The first, more common pitch called the knuckle curve, is really a standard curveball, thrown with one or more of the index or mean fingers bent. According to practictioners, this gives them a better grip on the ball and allows for tighter spin and greater movement. In all other respects, this knuckle curve is identical to the standard curveball. This version of the knuckle curve is currently used by Major League pitcher Mike Mussina, who also throws the other type of knuckle curve. ^*.

The second type of knuckle curve is a breaking pitch that is thrown with a grip similar to the knuckleball. Unlike a knuckleball, which spins very little, a knuckle-curve spins like a normal curveball because the pitcher's index and middle fingers push the top of the ball into a downward curve at the moment of release. Since only two fingers produce the spin, however, a knuckle-curve does not spin as fast as a curveball, meaning the break is less sharp and predictable. Because the knuckle curve can be thrown with the same general motion as a fastball, it is more deceptive than a normal curveball. This kind of knuckle-curve is rare - it is easier to control than a standard knuckleball, but still difficult to master. The most famous practitioners of this type of knuckle curve are Major League pitcher Burt Hooton, who played for the Chicago Cubs and the Los Angeles Dodgers pitching staff from the mid 1970s to mid 1980s. Currently, St. Louis Cardinals closer Jason Isringhausen and New York Yankees pitcher Mike Mussina throw this pitch Baseball pitches

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