It may not apply to this situation, but the first step is to really look and make sure that your son deserves to be there. Don't rely on what other parents or kids are saying. If they are friends or yours or your son, chances are, they won't be completely honest. They will not want to hurt your feelings or your sons.
If you and your son really feel strongly that he deserves more time, have HIM schedule a time to meet with the coach and or any assistant coaches and plead his case on a performance basis. You will never win the battle if you go at it from a personal standpoint. I have had some disagreements on a personal level with a HS coach, and I Know its difficult. Unless your kid is substantially better than any other options, he will be punished if you make it personal.