The taxi driver admits to breaking through the door to get at the girl, and admits to "giving her a touch" (hard to believe he calmed down much after busting down the door), so I have trouble believing the American man that "assaulted" the Korean man used any kind of "excessive" force. It sounds to me like the taxi driver got thrown, and not beat (punches/kicks). It would make sense to grapple with and throw someone if they were getting physical with a 3rd party. A chipped tooth and busted knee sound like injuries from a bad landing after a throw. If you punch someone in the mouth, their tooth won't chip like his did (see the picture on the original link). It'll break in half or come out all together. Aggressive assaults have injuries like black eyes, broken noses, knocked out teeth, broken ribs, and dislocated jaws. A chipped tooth and cracked knee cap with no other reported injuries, scream of "get the f- off, self defense".