Green’s Dictionary of Slang

(UK Und.) a fight.

1998		K. Sampson Awaydays 9: They’re not actively unfriendly, just silent — and quite psychotic in an off.
2001		N. Barlay Hooky Gear 31: Just provoke us into a massive off. Then they can do us for that.
2012		(con. 1980s) I. Welsh Skagboys 310: Nobody went that way but away fans and boys looking for an off.