tennis is clearly known and played in the "star trek" universe. in the "" episode , guinan comes to dr. beverly crusher complaining of tennis elbow. later in the episode, the doctor gifts guinan with a new, state-of-the-art tennis racket, which she is sure will alleviate her elbow problems. as it turns out, guinan was lying about playing tennis, but nonetheless the game is clearly known by the both of them, and the racket is real.