For the credit, how about:
Tiger
Tiger is nominally a ball game, but in places constitutes a full contact sport. It is an asymmetric game, consisting of two teams of four and twenty respectively (the "Tigers" and "Goats"). A normal game lasts one hour. There is a single goal in the centre of the field consisting of a wooden hoop raised above the ground. Tigers score points for every ball they put through the hoop. Goats cannot score points.
The ball starts with the Goat captain, who collects it after each successful goal. Tigers must then take the ball from the Goats in order to score. Tigers may capture the ball wherever it is, but are not allowed to hold the ball for more than five seconds - they must throw or kick it to another Tiger or into the hoop. Not doing so constitutes a foul. Goats may hold the ball if desired. Tigers can attack any Goat with the ball, for as long as they have the ball in their possession - by which one means they may literally attack them. Tigers are permitted any moves short of strikes below the belt or to the face in order to get the Goat to either release the ball or lose their footing. Any Goat who is knocked or falls to the ground (within 5 seconds of their possession of the ball) is out of the game. Goats without the ball may not be attacked, and doing so constitutes a foul. Goats with the ball (or illegally attacked) may defend themselves as they wish (sans hits to the face or below the belt), but Goats without the ball may not attack Tigers.
When the hour is up, the Tigers get as many points as they did goals. Goats get as many points as Goat players are left in the game. In the event of a tie, Goats win.
In summary:
* Two asymmetric teams: 4 Tigers, 20 Goats.
* The game lasts 1 hour.
* Tigers score goals by throwing the ball into the goal hoop.
* Tigers must obtain the ball from the Goats, and must pass the ball between players.
* Goats may do with the ball as they wish, so long as it stays within the field of play.
* Tigers can only attack Goats who have the ball, or are within 5 seconds of passing it on.
* Goats can only fight in self-defence.
* Goats who fall to the floor in any manner are out.
* Tigers win by ending the game with more goals than remaining Goats.
* Goats win by ending the game with equal to or more Goats than the Tigers scored goals.