There is a thunderous clattering as one shove turns 10 speeding roller skaters into a human avalanche of steel axles, spinning wheels and neon-clad limbs.
This is Anarchy in the UK, a two-day roller derby in London's Docklands. It is the first time a tournament of the sport has ever been hosted outside the US, and nobody has come to play nicely.
The shove in question was a "booty block", a move executed by smashing into another player as hard as possible with your backside. The bout has only been going five minutes and they're already on to their third major pile-up. This may be a sport for girls, but netball it is not.
The first game of the tournament sees the home team, London Brawling, taking on Montreal's New Skids on the Block. As it is the first bout London Brawling have played on the professional circuit, the scoreboard is pretty unforgiving. It is not even half-time, and Montreal already have 66 points to London's nine.
For those unfamiliar with the roller derby, it is basically a series of fast-moving gang muggings on wheels. Two teams of five skate at high speed in the same direction around a track. Points can only be scored by the "jammer" who tries to break free and lap the opposing team. The rest of the team try to block the jammer, using increasingly violent means.
Last year's Drew Barrymore film on roller derbies, Whip It, sparked an international surge of interest in the sport. Britain has gone from getting its first team in London in 2006 to having more than 80 clubs nationwide.
What began in America in the Thirties as a sedate game on roller skates played by both sexes has exploded into a cult sport for women. With punk-inspired outfits known as "boutfits", wrestling-style stage roles for women of all sizes, it has been embraced by many who previously wouldn't be seen dead doing sport.
The day's competition is as much about getting into character and pulling off some audacious smackdowns as it is about winning. With skate names such as Fox Sake, Kamikaze Kitten and Grievous Bodily Charm, it is clear nobody is going to be a shrinking violet.
Raw Heidi, aka Amy Ruffell, is on the track for London. The 28-year-old has a shock of blonde hair, a single black line of war paint on one cheek and a hard hat bearing her skate name in sparkling letters.
"A friend of mine asked me if I wanted to come and drink beer and watch girls slam into each other on skates. So of course I said yes and I've been hooked ever since."
The bout has an atmosphere more akin to an underground dogfight than an international sporting contest. More than a thousand people have turned up to cheer on the teams, though the volume of screaming makes it sound double that.
London's skaters spend a lot of the game sitting in the sin bin for illegal moves, the most dramatic of which is a violent shove from behind, causing a human pile-up that makes the M25 look like a bridleway. The track is marked out in hazard tape on the floor but there is nothing to stop the skaters careering into the crowd. In fact some have paid extra for the "privilege" of sitting in the hit zone.
Claire Andrews – or Boba Fetish, to use her bout name – is one of those who has paid for ring-side seats. She has travelled down from Cardiff with 20 of her club, the Tiger Bay Brawlers, to see the tournament. Despite her bright yellow and orange hair and lip piercing, the 24-year-old product designer is the most conservatively dressed member of her team.
"It's really big deal to have a proper WFTDA [Women's Flat Track Derby Association] tournament here," she says. Most of her team has never been into sport until now. "It really attracts an alternative crowd. There was a gap in the market for a sport for girls who don't like sport. Something active that gets you fit without involving anything lame like netball."
For some, the boutfits and skate names are a distraction from what they want to be seen as a proper sport. Stefanie Mainey, 29, is one of London Brawling's star players, but she is the only one who insists that the name on her back must be her own.
"I dropped my bout name because I felt they were taking away from the sport. They were making it a bit of a novelty when, as far as I'm concerned, it's very serious. It's a great sport that's really empowering for women. There aren't many team sports like this that are aggressive and predominantly played by girls."
As the referee blows the final whistle, the score is 57 to Montreal's 137, but London Brawling are undeterred. Raw Heidi staggers off the track. "I want a rematch", she says, grinning. "When can we go to Montreal?"