If I were up against someone with a chain, and I couldn't get away, I'd just cover the side which they were holding the chain (some thug is almost certianly going to swing from ouside to inside, not backfist it or whatever) and rush him. Once clinched, or even really close to that, a chain isn't so useful. Then it's headbutt time, or stabby time with my knife, or throat grabbing testical mashing time, well, you get the point.