When do you change ends on a tennis court?
when the number of games are odd
The analogy is asking to compare tennis to a court. To figure out the analogy, we must first figure out the relationship between tennis and court. Tennis is a sport played on a court. Boxing is a sport/activity done inside a boxing ring. The correct ending to the analogy would be ring. Tennis is to court as boxing is to ring. Tennis is played on a court. Boxing is done in a ring.
Water is not condusive to the game of tennis. The qualities of the tennis ball and the court change significantly in the presence of moisture, and thus a different style of play is needed, which is not considered good tennis. Matches could be played, however the style of game would change significantly and most people would content the outcome was not the product of fair play.