Table tennis is a sport where two or four players hit a ball with rackets back and forth to each other on a table, in a manner similar to tennis. The rules are slightly different, but the concept is quite similar. In singles play, the serve is not required to cross from the server's right-hand court to the receiver's right-hand court (or left to left) as it is in tennis. However, serving across is required in doubles play. Ball spin, speed, placement, strategy and tactics play an important part in competitive table tennis matches. The speed of the ball can vary from slow serves with much spin to smashes that travel as fast as 112.5 kilometers per hour.