Brambleball - How to Play

The Goal

Similar to much of Dwarvish society, Brambleball is very straightforward. Two teams attempt to push a 10 ft diameter stone ball as far into their opponents area. When time runs out, the team which has the ball on their side of the field loses. It is completely full-contact.
Brambleball is played on a 40'x40' square field that has been divided in half. At the start of the game, the ball is placed at the centre of the field, and both teams start along their respective back walls.
Traditionally, the number of players on each team is not set, and only depended on the number of people who wanted to play. However, it is generally considered bad sport to create heavily imbalanced teams; an unofficial rule that is taken just as seriously as the official ones by the Duergar.

In more modern settings, typically each team will have anywhere from 4 to 10 players.
Similarly, traditional Brambleball does not have a set time limit, and the game length is to be agreed upon by both parties before starting. Some historical games have lasted several days! Modern games typically adopt a time limit of 1 minute.

Mechanics

The ball is considered to have 4 sides (North, South, East, and West). Each side can have two medium-sized creatures or smaller (or one of any larger size) attempt to push the ball directly away from them. As a major action, a character may declare that they will attempt to push. At the bottom of Initiative, all characters which declared an attempt will make Strength (Athletics) checks. The sum of rolls made on all sides will be compared to the sum of rolls made on the opposite side (i.e. North and South, East and West). The difference between them, divided by 5 and rounded down, corresponds to the number of 6'x6' squares the ball will be rolled.
Additional characters can help push if there is an ally (or allies) in between them and the ball, if all of them also declare that they're going to push.
Immediately move the ball based on the differences in Strength (Athletics) checks. The larger difference is moved first. All characters immediately adjacent to the ball which attempted to push it automatically with it. Moving in this way does not provoke opportunity attacks. If a character did not contribute to the pushing, or the character cannot move, and the ball is moving into a square it occupies, on a DC 15 Dexterity Saving Throw, they can shift (move 1 square) out of the path. Characters which cannot move automatically fail this check. On a failure, they take 2d6 bludgeoning damage.

Example Round

Four people are playing Brambleball. On each of their turns, they have used their Major Action to declare that they will be attempting to push the ball. At the bottom of Initiative, the following Strength (Athletics) checks are rolled.
Red: 16 Green: 8 Yellow: 11 Blue: 18
These rolls are grouped and compared to each other based on their cardinal directions:
North-South Red and Green together have a total check of 24, while Blue has a total of 18. The difference between these is 6, which when divided by 5 and rounded down means that the ball is going to move 1 square to the north.
East-West Yellow is rolling unopposed, giving a difference of 11, moving the ball 2 squares to the east.
Because the difference in the East-West is greater than North-South, the ball (and all adjacent, pushing players) are moved first 2 squares to the east, followed by 1 square to the north. Any other players in the way of this path will need to make Dexterity Saving Throws to avoid it.

Pushing (D&D 5e Refresher)

Using the Attack action, you can make a special melee attack to shove a creature, either to knock it prone or push it away from you. If you’re able to make multiple attacks with the Attack action, this attack replaces one of them. The target must be no more than one size larger than you and must be within your reach. Instead of making an attack roll, you make a Strength (Athletics) check contested by the target’s Strength (Athletics) or Dexterity (Acrobatics) check (the target chooses the ability to use). If you win the contest, you either knock the target prone or push it 5 feet away from you.