Ooooo, good idea on the gladiator ring. Or battlegrounds... I don't know why MMO's don't do what L2 did with killing, if you killed, your name would turn slowly red, after maybe 4 or 5 kills, it would be solid red (this is ages ago before it all changed, not sure about now).
Being red would mean you couldn't go into ANY towns, guards would attack you on site, and any player who killed you, would not go red. So if you was spotted, it was a free for all and you really wouldn't last long at all.
To become white again you would simply have to die a bunch of times or do something else (can't remember... Farm? I don't know).
It was a simple mechanic that worked wonders. When there was a group of you farming mobs in cruma tower (oh the days in Cruma), you would see a group of reds and **** a brick. Those guys were out simply to kill anyone in their way. And we did the same, it was fun!