In baseball, a form of the fastball that is delivered by a pitcher angling and moving his arm horizontally, rather than in a vertical overhand motion.
All fast ball types can be delivered with a sidearm motion, as with the overhand, but the effect of the delivery changes the movement of the pitch. With a four seam fastball, rather than the ball seeming to rise vertically through the strike zone, the fastball moves inwards or away from the batter along a horizontal plane. There is a reduction in speed with a sidearm fastball, due not only to gravity and air resistance, but also because of the greater distance such a pitch travels as it moves along a wider arc. Nevertheless, the motion and the unfamiliar release point of the delivery makes a sidearm pitch still difficult to hit.
The sidearm pitcher (also known as a "sidewinder") is a rare type of pitcher in baseball, as most pitchers do not favor the unnatural motion of the sidearm, and not many coaches or managers understand the mechanics of the delivery.