I can't speak to how Newbury Park handles things specifically, but it's extremely common for high schools to require students to sign some sort of code of conduct or honor code form in order to participate in school athletics. I've personally never known of a school that didn't require something like that for extracurricular participation. It hopefully helps the coach out by providing some clear expectations for acceptable behavior, and also is meant to cover the school's butt in case kids do something common but potentially dangerous or illegal, such as underage substance use.
A code of conduct lays out school rules and expectations, but it isn't connected to state or federal laws, so breaking it doesn't require turning a kid in to law enforcement. It's similar to a kid breaking a school rule such as skipping class to hang out in the halls and then receiving a consequence such as detention.
Refraining from drinking or smoking while on a school trip, while using school resources, while acting as a member of the team, etc. is pretty much always a rule on these forms. If AS did actually get caught drinking at NXN (I have no personal knowledge either way), then Tonya and the AD would be expected to follow school policy by handing down the stipulated consequence, such as suspension or dismissal from the team.
We all know that many teenagers drink or smoke when they can get away with it, and I don't think it's some big moral failing in itself. However, it does lead to scenarios where high school coaches have to hand down consequences for school code-of-conduct violations not infrequently. That could very well be what happened here, not that L&L were just able to "vote" AS off the team because they don't get along.