Listen to their language, dominated by numbers (scores), names of cities and towns (arguably useful for geography) and words such as "aggregate" and "relegated", notable for their multisyllabic quality in a vocabulary that otherwise tends to be distinctly mono.
Observe what happens when they are near any item that could be interpreted as kickable. A banana peel? A challenge, but one worth taking for its comic potential. An empty Coke can? Even better - it's noisy. A piece of cake? A piece of cake, until it disintegrates on impact.
Then there's the talismanic trading of football cards. Otherwise loving and caring children have been known to pledge their grannies' heirlooms, if not granny herself, for a desperately needed Bergkamp or Giggs.
And of course, there's the near religious devotion to watching games, at the ground or at home, preferably in the company of fellow afflictees.
But these are externals. What really makes them a distinct race is their monomania. As Dr Faustus might have declared if he'd been created by Nick Hornby rather than Christopher Marlowe: "All is dross that is not premier league." Football is the air fans breathe, their raison d'etre.
It is also their social currency. While a small but growing number of girls dabble, there is a gender difference in approach. While football-mad girls can be enthusiastic and even obsessive about the game alongside other interests and modes of communication, for boys it's a different ballgame. It is their identity, their vehicle for bonding with other boys, perhaps the only one they have. It can make the difference between being one of the lads and being on the outside looking in.
Sam learned this a bit late. Attending a secondary school where, as in many, football culture was the dominant force among the boys, he found himself on the periphery. He wasn't particularly fussed about it to begin with. His other interests - music and tennis - sustained him, and his friendships with girls had always been strong. But as he entered Year 9, he felt more and more marginalised by the boys. If he wasn't to come across as a wimp, he'd have to adjust his public persona.
Being a clever lad, he found that by reading the sports pages and listening to the news, he could pick up the information required for those blokeish "conversations" that show that you know your league tables.
While he retains his individualism, he has found that knowing scores, fixture schedules and a few key names has brought him a credibility that had previously eluded him. He's learned how to play the game without having to touch a football.