A screwball is a baseball pitch that is thrown so as to break in the opposite direction of a slider.
Thrown by a right-handed pitcher
, a screwball breaks from left to right from the point of view of the pitcher; the pitch therefore moves down and in on a right-handed batter
and down and away from a left-handed batter. Thrown by a left-handed pitcher, a screwball breaks from right to left, moving down and in on a left-handed batter and down and away from a right-handed batter.
Due to this left to right movement of the ball when thrown by a right-handed pitcher, a screwball is used by right-handed pitchers against left-handed batters in the same way that a slider
is used by right-handed pitchers against right-handed batters.
There are several popular grips for the screwball, however this is probably the least important aspect. All that is required is that the fingers have a solid grip on the ball and adequately "grab" it during the period of rotation. Since the rotation is caused solely by the arm movement, precision finger placement is not required. That being said, one easy way to learn the grip would be holding the ball like a two seam fastball, and then moving the ball deeper into the hand. The pitcher's fingers should now arc over the ball (like it would with a curveball grip), but be directly behind the center of the ball (like a fastball). Putting the ball deep in the hand will not allow for proper "grab" on the ball and will provide maximum rotation (if thrown as suggested). If the ball is gripped with a standard fastball grip, the movement of pitch will be diminished and will be more like a fastball tailing inside to a right handed batter. Such movement may not be desired, depending upon the pitcher's goal.