Figure 9.

When throwing a slider, the pitcher attempts to mimic the arm motion and velocity used during a fastball while causing the ball to move in the horizontal plane. To do so, the pitcher begins to supinate his forearm during late acceleration through ball release (A), which generates counterclockwise spin (B) and right-to-left horizontal plane ball movement for a right-handed pitcher. In a left-handed pitcher, the ball will spin in a clockwise manner (C) and cause a left-to-right ball movement. When thrown properly, the ball will rotate around its central axis with spin in the coronal plane only.