Fraternities will have pledges take things. It’s very rare for it to be something stupid like socks. I’ve never heard it even be similar to that. A trophy from a rival fraternity? Something from the football field? A sorority composite? Yes, all things I’ve heard. Everything has a purpose, usually it’s stupid, it also wouldn’t just be one pledge. It’s all or none, All the pledges would have been made to steal the socks. This does not sound like a fraternity thing to me. Fraternities can be dumb, but not dumb enough to do something that would get a pledge caught so easily.