Goblin Football
(DS: Bjarni Egilsson, based on ideas from many sources)
Notes based on experience with the battle:

You can use any number of people; just split them evenly. 
This battle is best held in an open field (i.e., no trees or other obstacles). Mark out a rectangular field as large as you have room for, or as appropriate for the number of players participating. 
It is possible that not everyone will wish to participate (there are those who do not wish to play a goblin), in which case I suggest that combatants have their choice between joining this game and some "normal" battlegame or other activity occurring elsewhere at the same time. 
As in many informal football games, it is recommended that the defense wait 3-5 seconds before charging the line, and that the number of rushers be limited. 
Mark the boundaries as clearly as possible, including the outer edges of the end zones. Once a person steps out of bounds, they cannot re-enter that play. (You can't complain you were "forced out," since you have a weapon to take care of anyone who approaches, and of course no one is allowed to physically shove you...) 
Everyone who participated seemed to have a lot of fun with it! The fighting and adrenaline both run quickly. 
Rules:

All participants are members of two goblin clans which are at war over a most treasured object. (A tub of candy or something similar works well, and the team is welcome to do as it pleases with this treasure after the game.) To avoid injury to innocent family members and needless property damage to the villages, the leaders of the goblin tribes have agreed to settle their disputes on the football field. 
Membership in the clans (teams) will be marked by armbands, headbands, or war paint. For a football: if you have a foam or stuffed football, that would work great. Otherwise, make an elongated spellball, or use a normal spellball or throwing dagger -- anything that can be thrown and caught easily and safely. 
To score a point, a team member must have possession of the football beyond the opponent's goal line, without having stepped out of the marked boundaries. A touchdown scores one point, as does a "safety." There are no ways to score by kicking. 
More or less regular football rules apply (including things like "offsides" and "pass interference"), except that instead of tackling or blocking each other, each player has a single, one-handed, less than 4 foot weapon (hinged or non-hinged), with no armor, shields, magic, or projectiles. Any wound kills. Dead players are asked to signal their death clearly and quickly, and to do their best to avoid interfering with those who are still alive. Deaths last until the beginning of the next down. (See below.) 
After gaining possession of the football, a team has four plays to score. (If the field is large enough, there may be a certain distance they need to go to gain a "first down.") On the fourth down, they may choose to forfeit the ball by throwing or kicking it to the other team (this must be announced in advance). (Initial or post-scoring kickoffs are also conducted this way: the ball can be kicked or thrown.) 
Both leaders have huge numbers of goblins at their call. As players die, they are "replaced" on the next play by another family member who looks a lot like them. (In other words, the same Amtgardian, who is now representing a relative of the goblin who just died. Here's a good opportunity to roleplay.) All participants have one life per play, for as long as the game lasts. 
The game may continue as long as the reeve or the two captains are willing to let it, but a general guideline of one hour is recommended. At the reeve's or captains' discretion, teams may change ends of the field halfway through. (Halftime shows are optional.)