You probably haven't heard of the Fight Football League. By the time you finish reading this post, it will be your favorite sport.
Formed in Italy, the Fight Football League reminds one at first of something akin to rugby. Players move a ball by carrying or passing it up the field, scoring by getting it in a net at the end.
Then you notice they're wearing MMA gloves. That's because it's perfectly legal to beat the shit out of anyone on the opposing team, MMA style, whether they're carrying the ball or not.
It's more than legal; it's encouraged. If you knock out or otherwise injure a player, his team doesn't get to substitute for him. So instead of flopping around to draw a red card to put your team a man up, FFLers will simply pummel opponents into unconsciousness to gain a man advantage.
Here's a FFL promo video, and footage of an entire game:
For now, Fight Football exists only in Italy. That's fitting, because according to the organizers, it's inspired by an ancient Roman ballgame called Harpastum. A dubious claim, because the rules of Harpastum remain mostly unknown, but we'll let slide anything that lends legitimacy to a 20-man battle royale.