How to throw a screwball.
The screwball also known as the screwgee is a pitch that acts opposite of the slider or the curve ball, and breaks away from the batter. A left-handed pitcher would throw a screwball to a right-handed batter to break away from him.
The screwball was first created by Christy Mathewson, who called it a fade, as it faded away from the batter. Later on in history Carl Hubbell and Tug McGraw were famous screwball pitchers.
The screwball is released with many different pitching grips. Four seam, two seam curve ball. Most importantly though, it enables the pitcher to release the pitch while pronating his thumb downward, and turning his wrist outward, much like turning a doorknob. In doing so, a left-handed pitcher would be turning the doorknob to the right, or a right-handed pitcher would be turning the doorknob to the left, and pronating a thumb down to create this run or fade on the pitch.
The screwball has been known to cause arm problems. Fernando Valenzuela who threw a very effective screwball in the 1980's into the 1990's was known to have developed some arm trouble from this pronation of the wrist, or turning the doorknob as a right-handed pitcher to the right. In doing so, he put undue pressure on his elbow.
It's very important that pitchers, especially young pitchers, are aware of the risks of throwing a screwball.
These are some tips for throwing a screwball.