Sidearm

In baseball, sidearm is a motion for throwing a ball along a low, approximately horizontal axis rather than a high, mostly vertical axis (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 a high release point uses gravity to accelerate the ball, even as air resistance works to slow it. With a low sidearm release the ball is slowed threefold: by gravity (as it ascends), increased distance (because of its higher arc), and air resistance. But what the sidearm pitcher loses in velocity, he gains in ball movement and unusual release point.

In the middle of the nineteenth century, the game of baseball began to evolve from a sport played by amateurs for recreation into a more serious game played by professionals. One of the most dramatic changes was the transition of the pitcher's delivery from an underhand motion to an overhanded throw. Before the American Civil War, the pitcher's role was to initiate the action by offering an underhanded throw to the batter, in much the same way that a basketball referee offers up a jump ball to begin play. As the game progressed towards professionalism and became more serious, pitchers began to attempt to prevent the batter from hitting the ball by throwing faster pitches. The rules governing the delivery of pitches proved to be hard to enforce, and pitchers continued to stretch the boundaries of the rules until by the 1870s, the release point of pitches had reached the pitcher's waist level. As the game continued to evolve into the 20th century, pitchers' release points continued to rise to present day levels, although some adherents continued to use the sidearm delivery.

The various spins pitchers commonly employ--fastballs, curveballs, sliders, cutters—cause the ball to diverge from a "normal" trajectory. This is caused by the Magnus effect, which makes the ball move in the direction of its rotation. Batters learn these spins and their likely trajectories, but predominantly from high-axis pitchers whose pitches rotate around a mostly horizontal axis. Sidearm pitches rotate similarly, but around an approximately vertical axis. This causes common pitches to behave very uncommonly. For example, the four-seam fastball, when thrown by overhand power pitchers, seems to "hop", or rise on its way to the plate. This is because the ball is rotating backwards, lowering the air pressure above the ball. The same pitch thrown by the sidearm pitcher causes a horizontal rotation, and consequent sideways movement. Sidearm pitchers whose deliveries are below the horizontal throw a fastball that rotates nearly forward, so the ball will sink rather than rise.

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