Blackjack is an unusual casino came: skilled players with excellent memory can deny the house its edge. This is obviously a problem for casinos: it's an essential table game, but they can't very well just give away money. So they evict players who they suspect of using mnemonics or other "card counting" strategies that enhance their odds.
In this video, a "blackjack apprentice" named Colin captures hidden-camera footage of a casino pit boss sternly informing him that he is too good at the game to be allowed to continue playing it in that fashion.
If you're expecting to see the guy bounced roughly through the doors, though, you're in for a surprise. The pit boss is friendly and polite, and explains acceptable and unacceptable playing strategies--"Once you put a bet out there, you play that limit."--at fascinating length.
Colin is one of the Pros from Blackjack Apprenticeship, as well as the subject of the documentary "Holy Rollers: The True Story of Card Counting Christians." While filming for the documentary, he was followed by undercover cameras to capture what a real backoff is like. After counting cards blatantly for half an hour, this is what the casino did...