Revealing mistake: When Stiles enters the locker room, a guy walks out the shower and you can see his black underwear. (00:05:25)
Revealing mistake: When Stiles opens up his locker there are a pack of cards that have been spread out to give the effect of falling out of the locker as he opens but they are already hanging at first and then they fall with everything else. (00:35:15)
Revealing mistake: You see Scott walking towards the shower and he says hi to Chubby while passing him, but if you look closely after that you can tell Scott's only wearing a mask and his shoulder is bare skin. (01:00:15)
Revealing mistake: After the first game in the locker room, Scott notices a 6 inch long hair on his chest, the hair is visibly taped to his chest with scotch tape.
Chosen answer: Fake ID's are hard to come by. Its also difficult to make one look realistic by yourself.
Grumpy Scot
Styles is Mr. Popularity in a small town. Even if he did have a fake ID, chances are just about everyone knows who he is.