Sport is any competitive physical activity involving skill or physical prowess. Tennis is a racquet sport played individually or in teams of two. The object is to hit the ball back and forth over a net such that the opponent cannot make a good return. Tennis has evolved over time, with equipment like racquets changing from wood to composites, and balls changing from cloth to felt-covered rubber. There are also different scoring methods and strategies employed by different types of players. Famous tennis players through history include Roger Federer, Serena Williams, and Martina Navratilova.