In racquet sports, backspin (also known as slice or unerspin), is a shot such that the ball rotates backwards (as though rolling back towards the player) after it is hit. The trajectory of the shot involves an upward force that lifts the ball (see Magnus effect). While a normal hit bounces forward, when backspin shots bounce, they tend to bounce off the sides or even bounce up. This may make a receiver who has prepared for a different shot miss the ball when swinging. A backspin shot is useful for defensive shots because a backspin shot takes longer to travel to the opponent, giving the defender more time to get back into position. Also, backspin shots tend to bounce lower once they reach the opposite court, making them more difficult to attack. This is especially important in table tennis because one must wait for the ball to bounce before hitting it, whereas in tennis the opponent may be able to volley the ball.