Siegeball is a sport invented by /tg/ for DnD 3.5e. The game is roughly based on a combination of soccer, dodgeball and pinball. It's stupidly fast, horribly violent, and in other words, the perfect sport for PCs to join in. The game is handled identical to combat, with some exceptions. The rules are still a work in progress, and need playtesting.
More often than not, most towns will have their own variations on the rules, but they all use these rules as the base.
Siegeball is a game played between two teams. Each team consists of 5 players. One player of each team is the team's goalkeeper. Players must be unarmed, except for the goalkeeper. The goalkeeper gets a bat, which counts as a Club (Simple Weapon, One-Handed Melee Weapon, 1d4 Dmg(S), 1d6 Dmg(M), x2 Critical, 10ft. Range Increment, 3lb. Weight, Bludgeoning). The team's goalkeeper is whoever is holding the team's bat at the time, but there must be one goalkeeper, so players can pass the goalkeeper bat to other players, but they are not allowed to drop it. If the bat is dropped, a teammate must immediately pick it up.
Despite the official ruling that players must be unarmed, some arenas turn a blind eye to, or actively encourage, the use of weapons. Sneaking them into the field or having people in the crowd throw them in for the players is severely frowned upon.
Players may wear whatever clothing or armor they want, though most teams will have a uniform or theme.
Only attacks dealing non-lethal damage are allowed during play. Players may freely attack players of the other team, so long as they only do non-lethal damage.
Most cities do not allow magic on the field. Other cities only allow magic that 'buffs' or 'debuffs' fellow players, with flying and levitation usually being forbidden. There are some cities which allow free use of magic in any form.
Games of Siegeball require a special arena to be played in. These are usually either purpose-built for Siegeball, or erected temporarily inside a typical arena or colosseum.
The arena is a 155ft by 65ft field (31 squares by 13 squares), which narrows down to 35ft wide (7 squares) in the middle. It is divided into two halves by a 35ft square 'neutral zone' in the middle. The tip-off point for the ball is in the exact center of the arena. The entire arena is surrounded by a wall. The entrance gates to the field are at both ends of the half-way line.
Near the back of each team's half is their goal, a 5ft diameter pillar, known as the 'tower'. No official material for the tower has been decided as of yet, but it would most likely be either wood or stone.
Most towns and cities use the standard arena, but some use smaller or larger arenas, or different shaped arenas, according to local rules.
Each team starts in their respective halves of the arena, outside the neutral area. The goalkeeper must start inside their team's goalkeeper area. The goalkeeper is not allowed to leave the goalkeeper area.
The ball is possibly the most important part of a game of Siegeball. The ball is a magically enchanted orb of rubber-like material. It glows so it can be seen easily at nighttime, and it floats around 3 to 4 ft above the ground, making it easy to punch or kick.
The most important part of the ball is its 'momentum points'. These points dictate how far the ball moves, how much damage it does, and how hard it is to hit. The ball counts as a small creature, with a AC equal to 10 + its current 'momentum points'. The ball cannot be moved, except by attacking it.
When attacking the ball, the player attacking must decide what direction to hit it in. If the attack hits, instead of taking damage, the ball gains 'momentum points' equal to the amount of damage it would have taken.
While the ball has any 'momentum points', it moves forward in a straight line one 5ft square and loses one 'momentum point'. When it has no more 'momentum points' left, it stops. Yes, that's all in one turn. If it collides with an arena wall, it bounces off without losing any 'momentum points'.
If the ball hits a tower, it deals damage equal to its current 'momentum points', and rebounds as though it hit a wall.
If the ball hits a player, they can take an attack of opportunity against the ball. If the attack succeeds, any damage they inflict gets added to the ball's 'momentum points' and the ball changes direction to the direction the player chooses. If the player does not attack the ball, if their attack fails, or if the player has no attacks of opportunity remaining, the ball 'attacks' them with a bonus equal to half of its current 'momentum points'. If this attack succeeds, the player takes non-lethal damage equal to the 'momentum points' of the ball and must make a Fortitude save to avoid being stunned, with the DC being equal to the 'momentum points' of the ball. The ball then loses half of its 'momentum points' and bounces in a random direction. If the player dodges successfully, the ball continues on its current course without interference.
If the ball passes through a square adjacent to a player, they can take an attack of opportunity against the ball. This is the same as above, except failing to hit the ball does not cause the player any damage or affect the ball's 'momentum points' or direction.
Winning a game is simple. The first team to destroy their opponent's tower is the winner. However, the tower cannot be attacked directly by the players; all damage must be dealt to it using the ball.