Psyonix will in next few days test upcoming Tournaments mode for Rocket League's.
You can join the brackets now to test and to join in, right click on Rocket League in your Steam library, navigate to the Betas tab, and opt into 'tounramentsbeta.'
You will automatically download update and when next time you launch the game, Tournaments menu will be there for you.
Tournaments interface works as promised and you can also create your own tournaments, including private tourneys, with any mutators you like.
In the new update missing the ability to chat with participants while waiting for a tourney to begin and the option to spectate the rest of a tournament if you lose before the final round.
Interface haven't had any major problems while actually putting the most absurd mutators you can think of in place.