In discussing this scene/line in another thread, somebody pointed out that Blaine's form was off. His guard was too low for anyone with real training in boxing, especially someone who would likely be at a height disadvantage to most of his opponents. They intended this as an arguement that the line was a throw-away joke, I took it to be exactly the opposite. Because it answers the other big logic issue with there being a Dalton Fight Club. That is the secrecy. How did they deal with the cuts and bruses that would come with something like a Fight Club at a school that cracks down on bullying and, presumablly, violence, as hard as Dalton?
My headcanon is that, shortly after transfering to Dalton, Blaine got angry at someone. Angry like he got at Sam. They were alone, maybe with just a couple other guys. But instead of being broken up, the fight escelated. They beat each other up and the fight saps up the bitterness between them and suddenly Blaine's friends with this person. Though they both have to come up with covers for the nasty bruses and cuts. So when the cycle of anger starts over again with someone close to them, Blaine decides that what Dalton needs is a fight club, to deal with the pressure and anger and all of the other things. Except when it comes down to it, they can't excuse regular appearences of brusing and cuts...so in order to protect the members of the unoffical club Blaine founded, he tacked on an extra rule. No hitting in the face. All damage was done to places that would be covered by their uniforms. Thus, Fight Club at Dalton can work and Blaine's low guard is explained.