The rules for Shrovetide, or 'mob' football, are simple: 1. Each team tries to tap a ball against a goal three times, 2. The goals are set three miles apart, 3. As many people as would like can play at any time, 4. You are not allowed to use a car, or murder anyone. Everything else is fair play.
The game takes place over two days in Ashborne, England every year as a pre-Lenten tradition. And nothing but cemeteries, churchyards, and the town's memorial gardens are out of bounds for the game.
The contest dates back to the 12th Century, and local paper Derby Telegraph reports that teams are divided by a brook which runs through the town, with those born on its north side known as Up'ards, and those on the south known as Down'ards. Here's some footage of the two sides fighting in the brook back in the '70s:
[Derby Telegraph The Week Reddit