I’m questioning my reason for existence, with the faint ring of jazzercise echoing around my head. It’s 10am and I’ve circled the Clapham Common bandstand five times at this point, desperately looking for ‘the set of three rings’, as my friend mysteriously told me, amid hundreds of different sports happening on a Saturday morning.

I finally spot what I’m looking for, nestled between skaters, five-a-side football, and some joggers – the London Quidditch Club (LQC). I’ve come to take part in a taster session for quidditch to try and understand the community. But before my inquisition can happen, there are drills to be done. Sweating and battering into teammates under the panoptic gaze of Matt (who’s leading the session) I’m starting to have breathless flashbacks to secondary school rugby lessons.

I’m given a crash course on the rules of the sport. Three players on each team are chasers, trying to use a volleyball to score in those three hoops at each end. Two are beaters, throwing dodgeballs at players and forcing them to run back to their own goal if they’re hit. Then there’s a goalie, and a seeker, who chases after the snitch (a referee dressed in gold with a removable tag on his belt). You do all this with a broom – in reality, a plastic tube – pinned between your legs.

The first game of quidditch, at Vermont’s Middlebury College in 2005, ended in a 0-0 result. Neither the ‘Lesser Lovegoods’ nor ‘Avada Kill-Davra’ could score a single goal. In the years that followed, the fledgling sport exploded worldwide, spawning countless teams, leagues, and even a World Cup. Matt is actually a former New Zealand international. Each one of those nations has hundreds or often thousands of players and tens of different teams that play in domestic tournaments. London alone has three clubs, each with two or three squads. ‘It can be confusing for new people to come into,’ says Matt, especially those who arrive expecting, Harry Potter cosplay. ‘It’s not 15 nerds in capes throwing a ball around, it’s taken very seriously.’

Given the wizarding jargon, not to mention the faux brooms clenched really tightly between your thighs, it might seem that this sport is just the athletic arm of the Harry Potter fandom. But, as I’m told by one team member, Evie, half of the people who play the sport haven’t had much more than a passing interest in the series. ‘I often forget it’s anything to do with Harry Potter really,’ she explains. ‘It really is a sport in its own right… but it takes a certain kind of person to try it.’

Sitting under the soft glow of a faux-neon Guinness sign in the pub a few hours later, I start trying to put the pieces together. Frankie explains she was recruited a couple of years ago while studying in Vermont. Apparently, a lot of Americans assume an English accent makes you good at the sport because ‘It’s the real-life home of Harry Potter.’ Despite everything, though, she still hasn’t read the books. Simon, a new member, thought it would give him something better to do after a long week rather than ‘just sitting on the sofa and vegetating’. A lighting technician for West End plays, he’s full of stories about what it’s like to watch Hamilton multiple times a day.

Others joined because they were recruited by flatmates or because of similarities to dodgeball. For them, and everyone else, the selling point was being part of a community: not of obsessive Potter fans, but a sporting community with its own quirky, welcoming culture. Frankly, you’re more likely to find people discussing strategy for an upcoming tournament or joking about quiddcest than even mentioning Harry Potter.

On quiddcest: one of the alleged reasons Northern Irish quidditch is conspicuously absent from Team UK, I’m told, is because a Belfast quidditch team fell apart after all the players started sleeping with each other. One former player suggested the sport was almost like an aphrodisiac.