In baseball, sidearm is a motion for throwing a ball along a low, approximately horizontal plane rather than a high, mostly vertical plane (overhand).
Sidearm is a common way of throwing the ball in the infield, because many throws must be made hurriedly from the glove after fielding ground balls. An infielder's quickest throw to the bases is often from just above ground level, necessitating a horizontal release of the ball.
Sidearm pitchers, also known as sidewinders, are uncommon at all levels of baseball except in Japan, where sidearm pitchers are widely popular. Few find sidearm a natural delivery, and those who do are often discouraged by coaches who know little about sidearm mechanics, and who believe that overhand pitching affords greater velocity. This is generally true, since overhand pitching provides better mechanical leverage with which the body can use to accelerate the ball. But what the sidearm pitcher loses in velocity, they gain in ball movement and unusual release point.