Don drops the bo - Raph probably won't use it, and there are plenty of other ad-hoc weapons around - and uses the moment of surprise to duck out of the attack and back-spring away.

Once again having created some distance, he quickly takes stock of the situation: they're both bleeding, the carefully-sorted piles have been kicked all over the place, he's going to lose, and it's all over a stupid argument, which he's probably also going to lose. Somehow, none of this makes him want to give in.