On my server I had my own Arena system (as I didn't really believe in most of plugins what I found here, and I still think that if you want to create something really cool, you'll need to do some coding).
It was working like this - I had 2 arenas build far away from players, and of course secured with my Zone plugin, so nobody could destroy it or build near.
Player was opening game, other was writing "/arena join" and if everything was ok they were teleported to one arena. I don't remember if I ended removing and giving back of inventory, but it was in development for sure. I remember that I was also preparing 2vs2 game.
People loved my server for things like that - many custom plugins, more entertainment.
But guys remember - it will change fast if some cheater will join that match and ruin it. That's why I closed my server - people was mad at me because I couldn't "add proper anticheat", they didn't care about how many plugins I made to make that Rust more cool for them.
Yesterday I was playing on some new polish server and I saw there that unaware admin what I was on first days off my server. He just didn't know how many cheaters are on his server right now. I wonder how many time it will take for him to close it