Every year something strange happens in southern Australia. A significant proportion of it’s population get involved in a celebration of tribalism. It’s not about ethnicity – the population of Melbourne, the centre of this cult, is pluralist and ethnically diverse. But until recently each suburb of Melbourne was represented by a gang of tough skillful men who went out each weekend and beat one another up.

Nowdays the demands of marketing have spread the teams around the country, but the principle is the same. Normal citizens who are devotees of this cult adorn themselves with the colours of their gang, and watch on the television or at the stadium, each weekend, as their representatives spend several hours in physical combat with the representatives of another tribe.

This has a long history with Celtic peoples. The Battle of Moytura in 1272BC was fought after a particularly bloody hurling match between the Fir Bolg and the Tuatha de Danaan. All that same energy is present today – a friend of mine had his ashes scattered on the team’s home field by his tearful and equally footy-obsessed mates – and it all culminates on one weekend each year.

This weekend. Today.

Geelong is an industrial town about an hour from Melbourne. Port Adelaide is the working class centre of the capital of South Australia. Teams from these two places are staging the final battle of the year, just this afternoon at the Melbourne Cricket Ground in front of 120000 screaming atavists.

It’s a simple, violently physical game involving 36 players kicking and punching an oval ball up and down a large green field. Or rather this is the catalyst for the real game, which requires that half the population of Australia drink beer and scream and cry as they get in touch with their inner caveman.

The other half steer clear of the whole messy business.