Many events includes killing, last man standing, just killing or other types requires you to kill others, and since its not town control fight, people from npc factions are taking part in them. For example i am vault city citizen myself, i take part in event, then after it i look at my karma and i have -1500 reputation with vault city citizens for just taking part in event :/ I think there should be option for gms, to freeze all reputation changes in place where event is taking place. Dunno if it is possible to be made for developers, but still something like this is urgent to have.