A screwball is a baseball pitch that is thrown so as to break in the opposite direction of a curveball. 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 in on a right-handed batter and away from a left-handed batter. Thrown by a left-handed pitcher, a screwball breaks from from right to left, moving in on a left-handed batter and away from a right-handed batter.
Screwballs have become increasingly rare because they require an awkward arm motion that is both difficult to master and demanding on the arm. Very few Major League pitchers throw a screwball; many now throw a changeup that emulates the pitch's movement, however.
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