A knuckleball is a very rare pitch, and the pitchers who throw it during games tend to use it almost exclusively. The goal of a knuckleball is to eliminate almost all of the spin on the baseball, causing it to flutter unpredictably on its way to the plate.
Although knuckleballs come to the plate at a much lower velocity than the average pitch, they can be among the hardest pitches to hit because they move so erratically. (They are also among the hardest pitches for catchers to catch and for umpires to call.)
The obvious downside to the knuckleball is that if it isn't "dancing" -- or moving -- it becomes very easy to hit because of the slow speed of the pitch. Because the pitch is so hard to master and the risks of throwing a bad knuckleball are so great, very few pitchers throw the knuckleball -- typically no more than a handful of Major Leaguers have done so at any given time in history.
The knuckleball gets its name from the typical grip used to throw the pitch, with the knuckles either on the ball or hovering just over it while the fingernails dig into the surface. The pitch is thrown with relative ease, and as a result, knuckleballers typically have the least strain on their arm of all pitchers. They can often pitch deeper into games and without as much rest in between starts. They frequently pitch into their 40s, without as significant a career decline as a typical hurler.
It's unclear how the knuckleball came into existence, but Eddie Cicotte, who pitched from 1905-20, was given the nickname "Knuckles" for the unconventional way he gripped the baseball, and many believe he was the first to throw the pitch regularly.
Watch: Steven Wright picks up a strikeout on a knuckleball.
In A Call
"knuckler," "flutterball," "dancing knuckleball," "dry spitball"