It's above your pay grade. Respectfully tell them it's not your department and they should talk to their kid/coach/ad.
There are rules about eligibility for grades and such - but I think that only applies to games. In our town, ineligible players can practice. As far as I know, there aren't any rules regarding player selection - that's on the coach.
Player selection is always a thorny issue. To an educated parent, it sometimes makes you want to gouge your eyes out. I have seen some wild things. My kid's basketball tryout didn't even include shooting. Then they wondered why the game was over when they got down by 5 points or more. Baseball is a few days away -- hopefully they will included hitting.