The knuckleball—also known as the knuckler, the fingernail ball, the fingertip ball, the flutterball, the floater, the dancer, the bug, the butterfly ball, the moth, the bubble, the ghostball, the horseshoe, the dry spitter, and, curiously, the spinner—has been around, in one form or another, for nearly as long as professional baseball itself, though for much of that time it has been regarded with suspicion. Spinning is precisely what it does not do. In fact, a lack of spin is about the only identifying characteristic of the pitch. There is no right way to hold a knuckleball when throwing it (seams, no seams; two fingers, three), and no predictable flight pattern once it leaves the hand. “Butterflies aren’t bullets,” the longtime knuckleballer Charlie Hough once said. “You can’t aim ’em—you just let ’em go.” The pitch shakes, shimmies, wobbles, drops—it knuckles, as they say. Which is doubly confusing, because the term “knuckleball” is itself a kind of misnomer, a holdover from the pitch’s largely forgotten infancy.

http://www.newyorker.com/magazine/2004/05/17/project-knuckleball