They are arch rivals of Team South.
The team was set up for the Good Good Friday 2 ("GGF2") Join MEet, for a North versus South "friendly" challenge football match. This has since become an annual contest with a trophy, the Joinee Cup awarded to the winner, which team retains possession of it for the following year.
There is no precise definition of the border between north and south. Also, some players choose to play for the side representing where they live, not where they are originally from; hence the chant, "Scotty is a Judas", made at Joinee Scotty Iscariot, the supposed Scot (who's really more like a Texan) who in fact plays for the south due to living in London. When he can be bothered to turn up at all, that is!
Since GGF3, the referee for the match has been Captain K, deemed to be the only Joinee available who was sufficiently fair, impartial, dandy, and cross-border to be able to perform the duties fairly! (He is from the south of Scotland but has lived in the north of it, and has also lived in the south of England, though he now lives in the north of it...)
The GGF5 match saw Team South unable to fend a full 11-person team, so Team North nobly began the game with an equal number of players, although with the benefit of subs being available. Captain K was unable to attend and so did not referee this match.