By Alison Freeman
BBC News, London
A school hall in Chalk Farm might seem an unlikely venue for a sport linked in many people's minds to the frightening 70s' film Rollerball.
Roller Derby is a huge sport in the United States
But it is where north London's newest roller derby group - the Rockin' Rollers - hold their weekly practices.
The all-women team dress in fishnets under the knee pads.
And rather than killing opponents as in the film, players block and bash each other as they speed round the track.
Jean Brady's skater name is Evil Jeanius and she has been part of the team for the past six months.
"The aim of the game is not to hurt someone fatally or anything like that," she explained.
"It's about bumping and going back to the tom boy days in a sense, while still looking quite sexy - at least we hope so."
The sport sees two teams competing to score points.
The teams make up a main pack which skates around a track.
They each have a jammer - a speed skater whose job it is to get past the main pack.
Each team has to try to get in the way of the opposite team's jammer, while at the same time clearing the way for their own.
The result is lots of jostling and falling over, sometimes with damaging results.
During the practice, a woman gets a split lip crashing to the floor and I am told that another team member recently ended up in hospital with a broken elbow.
But the players accept this as a risk of the game they clearly love.
In fact when questioned, most of them agree that the sport appealed to them in the first place because it allowed them to let off the steam they build up during their busy London lives.
"It's a theatrical thing," said Evil Jeanius.
"It's about entertainment for the crowd, that's what we are heading towards.
"That's what they do in America where we've got the idea from.
"We are to trying to entertain the crowds so there will be maybe some fighting involved, but it would be kind of theatrical.
'Bigger and better'
"For Halloween we had a lot of face paints and we'll have silly pants under our skirts and we pull them up to show the crowds. It's like wrestling."
She said that the team was desperate for more players to create a "bigger and better" experience for the crowds.
In the US the sport has really taken off, with the all-women teams having a huge following.
Roller derby may not be for the faint-hearted, but any women who are thinking of taking part might be interested to know that you can burn off 500 calories an hour playing the sport.