I agree that a spin (whether intentional or unintentional) is probably there. Of course, the best option would have been to closely monitor who showed up at your party.
I can honestly say I never attended a party that was so large that people just escaped unnoticed or people arrived just to do violence. From what it appears, that might be a party pasttime I didnt know about.
But assuming these facts to be true, if you are engaged by someone out of your weightclass with no provocation on your part, who is beating you to a pulp, do you take it or if you happen to have a gun, is it underhanded to shoot?