Tennis is a racket sport that is played either individually against a single opponent (singles) or between two teams of two players each (doubles). Each player uses a tennis racket strung with a cord to strike a hollow rubber ball covered with felt over or around a net and into the opponent's court. The object is to manoeuvre the ball in such a way that the opponent is not able to play a valid return. If a player is unable to return the ball successfully, the opponent scores a point.