In sports, in particular racquet sports, topspin is a property of a shot where the ball rotates as if rolling in the same direction as it is moving. Topspin on a shot imparts a downward force that causes the ball to drop, due to its interaction with the air (see Magnus effect). It can be generated by hitting the ball with an up-and-forward swing, with the racquet facing below the direction it is moving. A topspin shot is the opposite of the slice; topspin itself is the opposite of backspin.
On most court surfaces, topspin also makes the ball bounce higher. As a result, it is often used on clay or "soft" court surfaces which have a naturally higher bounce, in order to make the ball harder for the opponent to hit. An opponent with a one-handed backhand is especially vulnerable to a topspin shot because it is difficult to hit a high ball with a one-handed backhand.
The topspin shot is primarily used by tennis players as either a "safe shot" or rally ball, or it can also be used to construct a point. For example, a player may hit three topspin shots crosscourt, and then on the fourth shot hit a flat ball or a slice down the line to set him/herself up to win the point.
In tennis because of a net being in the middle of the court, using topspin will increase the player's consistency. Hitting low to high as the player approaches the contact point will impart lift. Keeping the racket face (the strings) slightly closed from perpendicular will impart the topspin to the ball that the player wants.
In Cricket, a topspinner is a type of delivery bowled by a wrist spin or finger spin bowler with top spin, so the ball falls earlier and faster than normal. As a result, the ball drops shorter and bounces higher than might otherwise be anticipated by the batsman.
In competitive Table tennis, effective command of topspin is indispensable, not only in order to be able to execute an attack shot counter to a backspin ball, but also in order to be able to execute a speed shot when the ball is already lower than the net.