Based on comments above and what I suspect is true, you'd have to convince a jury that your force was justified. If you can convince them that you believed the guy's life is in danger, based on the viciousness, severity and duration of the attack, and then whack them on the head with a baseball bat, and send them into a coma for life, then you will likely be OK. Unless there's a civil suit of course and your wages are garnished for life for the family in terms of "damages". :-P