underspin

Underspin, commonly referred to as backspin, is a rotational state of a moving ball in which the ball spins opposite to its direction of travel. The term is used across several ball and cue sports, most notably table tennis, tennis, and billiards, and in other contexts involving backward rotation imparted to a projectile.

Production: In table tennis and tennis, underspin is produced by brushing the ball on its underside or by a slice that opens the racket face so that the top moves forward and the bottom pushes backward. In billiards, underspin is created by striking the cue ball below its center with a downward stroke, causing it to draw back after contact. The specific technique varies by sport but the result is a ball with backward rotation.

Effects: Backspin tends to slow the forward flight and, on contact with a surface, produces a low, skidding bounce. In table tennis and tennis, underspin can prolong the ball's time in the air while keeping it difficult to attack with a strong offensive shot. Players often counter with topspin or lifting strokes to overcome the spin, or use further spin to deceive the opponent.

Notes: Underspin is contrasted with topspin and with sidespin. In tennis, slice shots produce underspin; in billiards, backspin is used to draw the cue ball. The term underscores the relationship between spin direction and trajectory that governs control and strategy in spin-based play.