Dear parent,
First of all ask yourself whether frustration has ever helped to bring about positive change. Does your son get significantly less playing time than other kids?
Nonetheless, if your son is as keen a ballplayer as you describe him, he should go to the coach and ask him: Coach! I really love this game, what can I do to get more playing time so I can develop myself even better? Sometimes this is the true lesson to be learned ;)
Good luck and play ball!