That's a rather serious injury from the looks of it. He needs to be kept in a small cage with food and water within easy reach, protected from other chooks and too much sunshine but allowed to see them and get some sunlight on him (vit D helps heal) and left in peace until he can heal, if he's able. I have seen something similar in a hen but hers was worse. She could walk, but her tail was touching the ground nonstop, and she died not long after. He's a smart boy to try to avoid walking with that problem. I wouldn't handle him any more than absolutely necessary, because with an injury that bad you don't know what's gone where and don't want to rearrange his bone structure if avoidable. I would guess it is a spinal injury. Since a lot of their spine is fused, they're less likely to be paralyzed than we are. But he needs help. Best wishes with that.
He may make a full recovery, he may make a partial one, he may not make it, but it's up to you as to whether or not you put in the time and effort to help. No condemnation if you don't choose that. Personally I would put in the time because I want to know what the survivability of the issue is, so if it occurs to one of my best I know whether or not to expect a recovery. But everyone's circumstances differ.
