This was a sort of Team LMS PK that Delteria and NPulse had, and UN had a variant of.
Players divided into two or more teams, usually randomly but that's not important. Everyone is set to .5 hp, and that's it. The team with the last player left wins. Usually it's played with just swords, but NPCs or throwable objects work too.
With a lot of players this could take some time, but with just a few it goes by quick, so I'd say with bigger groups to just have one round, but that's just my take. First team to three wins sounds decent too, to prevent it just being a quick tix event.
Ranger hosted it today in the allstar spar room, problem is that that is spar only so no NPCs