From the Super Mario Wiki
The Composition Court is a tennis court from the Game Boy Advance game Mario Tennis: Power Tour. This court is where the varsity-ranked players play. After Clay and Ace play here, they move up to play at the Island Open. It is a green, indoor court with a surrounding miniature, white fence that runs along a yellow floor. Also, there are windows facing the court.
Mario Tennis: Power Tour
In Mario Tennis: Power Tour, when players are on this court, it is mentioned that the tennis ball travels faster than it does on any other court. The ball's bounce height, however, is normal.