Screwball and Knuckle Ball Basics
The screwball, or reverse curve, is thrown in a manner similar to the delivery of the sinker, except that the wrist is snapped as the wrist rotates inward. Actually the screwball is thrown exactly like a curve except that the wrist is turned in the opposite direction.
The knuckle ball is delivered with the first two fingers poised on top of the ball, the fingers being cramped right back as far as they can be bent. Actually then the hand is behind the ball. And when the ball is thrown it is pushed off the fingers instead of being spun off the tips. In throwing the pitch you must take care not to cock the wrist, as you do on every other pitch. Keep the wrist stiff, almost as if you were putting the shot, and you will find that the ball does not spin at all.