Yeah, Rocket League is out on Xbox One next week, but if you absolutely must play it on Microsoft’s console today, a pretty decent version of it has been made using Halo 5's editing tools.
It’s far from perfect—the pitch has spots where the ball can get stuck, and the physics gets weird sometimes—but then, this is an editor designed for first-person combat, not car football.
On the plus side, it allows for up to 16 players, and those 16 players can get out of their vehicles and shoot things, so it’s got that going for it.
There’s more info on the map here.