Pickleball is an indoor or outdoor racket/paddle sport where two players (singles), or four players (doubles), hit a perforated hollow plastic ball over a 36-inch-high (0.91 m) net using solid-faced paddles. Opponents on either side of the net hit the ball back and forth until one side commits a rule infraction. The appearance of a pickleball court, and the manner of play, resembles tennis, but the court is the size of a doubles badminton court. Court lines and rules are specific to pickleball and include two 7-foot areas (2.1 m) on either side of the net known as the non-volley zones, where the ball cannot be hit with the paddle unless the ball bounces first. The official rules specify side-out scoring, where only the serving team can score a point. All serves are made with an underhand stroke. The hard plastic ball used in pickleball produces significantly less bounce than softer flexible balls, such as a tennis ball.