Table tennis is a sport in which two or four players hit a lightweight, hollow ball back an forth to each other with paddles. The game takes place on a hard table divided by a net. Players must allow a ball played towards them only one bounce on their side of the table and must return it so that it bounces on the opposite side. If the ball doesn't land on the opponent's side, it is a "dead ball," unless the receiving player has hit the ball before it has clearly passed the end line of the table. Play is fast and demands quick reactions. A skilled player can impart spin to the ball, which makes its bounce and reaction on the opponent paddle or racket difficult to predict or return with confidence.