You're digging yourself deeper into a hole here. The jaw and nose are very fragile. Trayvon Martin absolutely could have knocked Zimmerman out with one well-placed blow. Move your jaw from side to side: feel how little give it has? Force it to move an inch too far and it breaks. It's less a matter of force and more a matter of placement. Your argument simply defies science at this point, assuming a broken jaw has a high chance of leading to temporary unconsciousness (it does).
Even if, it only enhances my point that Zimmerman wasn't in any real danger.
If it was easy to break his nose and bust up his jaw, and Martin couldn't do it (probably because, as I've said before, he was a skinny arse 17-year-old) then how much danger was Zimmerman really in?
The only reason I went down this road is because NC claims that he, as a 17-year-old, could easily take down a guy with one punch. Great for you NC. Most people can't, not the last of which was Trayvon Martin.