The problem with bundling it in with your combat skill, or your strength stat, is that(as someone else points out) it makes strong characters tough as well.  I want to separate a character's ability to [i]give[/i] damage from their ability to [i]take[/i] damage, so that characters will have to choose which to focus on.  So I think I will add a new stat for it.  

I'd [i]like[/i] to add in armor as well, but I still need an adequate drawback.