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1.
A game played by school children, involving beating the fuck out of each
other with various weapons made of tied up school jumpers.

Usually played in a set defined area with a few players, in teams, tag
teams, or free for all, or less commonly as giant class vs class battles,
featuring each side charging at each other across the playground with as
many as 60 children in one fight.

There are few rules other than batter each other with your jumper weapon,
with winners only being determined by one side surrendering.

The two main weapon designs were clubs - where the jumper is laid out flat,
the torso rolled up and tied leaving the sleeves as handles, and whips,
where the jumper is knotted at various points and swung by one sleeve to
create a whip type weapon.
"Alright lads, lets play jumper wars!"
"Mothers are commonly angry about the stretching caused to jumpers by playing jumper wars"
"The teachers were bemused at the sight of two armies of children charging
at each other swinging their jumpers in some kind of jumper war"
by Dr Pot November 02, 2013