So the school can regulate behavior on school property. If they catch them smoking at school they can kick them off the team because smoking on school property is against school rules. And even then, because they are a public school, they are bound by the 4th Amendment in enforcement.
The school wants to regulate what they do outside of school, and that's mission creep of the legitimate use of loco parentis.
The schools are acting in loco parentis.
I'll remind you of that when they're telling your kid that it's ok that Heather has two mommies, and teaching them the joys of fisting and condom use. Be careful what you wish for, you just might get it. You're putting a great big club in the hands of the 400 pound gorilla of government. One day, he'll have a new master, and he'll come swinging for you.