I'm so sorry to hear of your son's challenges (and yours as well).

Anger and rage are common problems with TBI. The areas of the brain that control primitive emotions are located more to the periphery and to the front. As such they are more liable to be damaged by physical trauma. The more primitive drives are towards the center of the brain, which are hence more cushioned. Do a search on "traumatic brain injury" and anger, a lot will come up.

This very likely explains why your son is struggling with anger issues. As for what to do about it, of course this is the tricky part. I have this problem, and find the only thing that works is go for a "time-out" and let the feelings subside. I mean no contact with other people at all. It does take time. Sometimes a few hours, sometimes days. Not easy.

Best of luck and well-wishes to you.