Purple Drank isn’t illegal if you have a prescription for cough medicine. Are people presumed innocent until proven guilty in a court of law, or does the Raiders want to hold its players to a much higher standard? (How well do the other players meet that standard?)
Normal people do not make prescription drugs into recreational beverages. And since many derivatives of this are made from codeine, it is very easy to conclude that most of its usage would be in violation of most workplace anti-drug policies.
I think more than anything else, even his own teammates would shun him over purple drank, because its sleaze factor is just so low rent that it is positively embarrassing. There is a lower class scale to things, and purple drank rates right down there with chugging Afrin.
http://blogs.houstonpress.com/rocks/purple_drank.jpg