The term 'STARTS A TENNIS GAME' can be solved by the word 'SERVES', which is a 6-letter word. In tennis, the serve is the first shot of the game and is used to start the point. The server stands behind the baseline and hits the ball over the net into the opponent's court. The server must hit the ball diagonally across the court and the ball must land in the service box. If the serve is successful, the point begins.