Sadly I don't know if a plugin like this is possible, because of pvp being false or true in the server properties, but here's the idea. PVP option maybe? You turn it on, you can attack and be attacked. Turn it off, you can't. If you've attacked someone, you can't turn it off for an hour or so of play time. Something like that. You can turn on pvp or turn it off, and if you've attacked you are a flagged pvper for an hour or so, until you are done attacking people. A simple exception so people can't abuse /pvp on and /pvp off. Just an idea, let me know if this is a plausible plugin request. Thanks to ALEX from theminehub.net for submitting this idea.