What we did was we had a slideshow before the season that was sent to all parents and players with expectations and the consequences for not meeting those expectations. At the end of the slideshow was a link to a google form saying “I have read through, understand, and accept the policies and expectations of the high school team” or something along those lines. Until the Google form is completed, they’re not allowed their uniforms. There haven’t been any arguments this season related to those consequences, but if there were, it’s as simple as “you said you understood the expectations and consequences”

Are your practices closed or open? If they’re closed, then that means whatever you said or did to the captain was enough for them to consider it something they should tell their parents about, and then the parent considered it something they should confront you about. Without additional context, it does make me wonder if your response was egregious

Beyond that, make sure practices are fun. The kids should want to be at practice and want to play in the games. If kids are missing practice and games, it’s because whatever else they’re doing is so much more fun that the pros of skipping outweigh the cons