21 points system
1. A game is played to 21 points.
2. The side which won a rally adds a point to its score, regardless of whether it was the serving side. Under the 15-point system, only the serving side can increase its score.
3. If a game is tied 20 all, the side which first wins 2 consecutive points wins that game. Unlike the 15-point system, there is no set.
4. If a game is tied at 29 all, the side which wins the next rally wins the game 30-29. Consequently, the maximum score of a game is 30.
5. Serves alternate between sides. The serving side continues to serve as long as it is winning the rallies. As soon as it loses a rally, service immediately passes over to the opposing side. Consequently there is always only one serve, even in a doubles game.
6. When the serving side wins a rally, the same server serves again but from the alternate service court. This results in the players on the serving side changing service courts and is the same as the 15-point system.
7. When the score of the serving side is even, the serving side serves from the right service court. If the score is odd, the serve is from the left service court. This means when service changes from one side to the other in doubles play, the first serve can come from the left service court, which never happens under the 15-point system.
Doubles play also abides by the following rules:
1. When the serving side wins a rally, players on the receiving side do not change service courts. This is the same as the 15-point system.
2. When the serving side loses a rally, none of the players changes service courts. This is the same as the 15-point system.
3. If players commit an error in their service court positions, the error is corrected when the mistake is discovered but the score still stands.
