It's a really great moment when you find your name," says Christine O'Connor. "It's a really big deal ? it's like, who am I going to be now? It's the opportunity to leave yourself behind, and just go."

Christine is a 30-year-old children's book buyer for a national chain who lives with her fiancé. Shortly, she will don a short skirt, fishnet tights and a pair of specialist roller skates, in the process becoming Kitty Cadaver, one of Ireland's first rollergirls. Flying around an oval track doing her best to bodycheck her female opponents into a sprawling heap, the name is emblazoned across her back. "I was going through names for weeks, writing them down, seeing how they worked. Kitty Cadaver just came to me, and I love it. I tend to go by Kitty a lot of the time now."

Roller derby is a sport with a strange history. It emerged in the 1930s when sports impresario Leo Seltzer tried to capitalise on the popularity of the roller skating endurance races that were drawing crowds in the US. Seltzer took this concept on the road, on a large portable track, playing to crowds of thousands every night. One day, sports writer Damon Runyon was in the stands, and – noticing that the crowd enjoyed the crashes and falls more than the bits in between – persuaded Seltzer to alter the rules for maximum theatrics. Skating became a full-contact sport, and roller derby was born.

Derby saw its heyday in the early 1970s, with teams like the San Francisco Bay Bombers and the Northeast Braves clashing in front of stadium-sized crowds of 30,000-plus. Television audiences peaked at 15 million a week in 1969 for top stars Ann Calvello and the Blonde Bomber, Joan Weston. But then in 1973 it all ended. Citing high overheads and the Arab oil crisis, Seltzer shut down his derby league, the sport disappeared from TV screens, and its superstars went off to find other jobs.

Today, however, roller derby is enjoying an unexpected comeback. A group of independent-minded women in Austin, Texas formed a female-only derby league in 2001. Helped by a reality TV show called Rollergirls, the grassroots movement took off at speed: by 2006 there were more than 100 groups. The sport reached cinemas earlier this summer in the Drew Barrymore movie Whip It – named after a signature derby move – and now there are 541 official leagues across the world from Belgium to Brazil. Almost all are female-only.

Dublin Roller Girls – Ireland's first official league, though with the ladies of Belfast, Cork and Galway hot on their heels – was founded in September 2009 by eight women who met on an internet forum.

Almost a year later, in the corridor of a community hall in Inchicore on a sunny Monday evening, a transformation is underway. Girls arrive in tracksuits and runners, then suit up in short skirts, tight-tops, flamboyant eye make-up.

Each woman straps on a formidable set of safety equipment. There are knee pads, elbow pads, wrist pads, helmets and mouth guards. "All of this is required," says the league's coach and referee – and Kitty's fiancé – Christopher Goggins. "You get sent off the track if you don't have it. But you can also get shin guards, padded shorts..." "Boob protectors," someone else chimes in.

And then there are the skates. They must be 'quads' – with two sets of two wheels – rather than rollerblades. Almost every woman wears specialised derby skates, which can cost hundreds of euro.

Inside the hall itself, the noise is deafening. The clatter and squeak of skates on wood, the referee's shouts and whistles and the laughter of the rollergirls all echo from the high ceiling. The girls go through a series of complex drills – including a particularly fearsome one known as Satan's Mattress – and begin skating around an oval track, marked out with cones. In a pack, they turn the corners like speed skaters, crossing one leg over the other; and you can see the pleasure they take in the smooth movement. "I just love being on skates," Kitty says.

After a while, coach Christopher blows his whistle; the girls huddle in the centre of the track, and the real practice begins. Roller derby is played in two teams. One skater from each team is the 'jammer'. It is her job to outpace her counterpart and overtake as many of the other team as possible, scoring points in the process. The rest of the skaters – the 'blockers' – aim to help their own jammer and impede the opposition, which is where the contact comes in: girls use their shoulders and hips (sometimes known as "booty blocking") to hit rival skaters, with the aim being to send them sliding and sprawling off the track. Each team also has a pivot, who keeps them together and sets their speed. ("The pivot is like the mammy of the pack," one girl tells me.) Played in frenetic two-minute bursts, the derby is gripping to watch, and it's true: the collisions are the best bit.

Getting hurt is an integral part of life as a rollergirl. According to bank worker Ailish Byrne – aka Whippy Longstocking – the first thing any skater learns is "how to fall. You practise one-knee falls, double-knee falls, the baseball slide." Fishnet burn can be a particular problem.

"It's like Fight Club," says Liz Clonan – Agent Provocative – who is a legal executive for a large law firm. "You go into work bruised up one day, limping the next."

Every rollergirl, all over the world, has her own individual derby name; and all the names are registered on a central Master Roster. The list contains 19,974 rollergirls at the last count, from Alevia Bleeding to Zarathrustya (Greater Jacksonville and Red Stick Roller Derby, respectively).

The names can transform people, Kitty says. "You're taking on, not a persona, but... Some people would be much quieter when you talk to them in person, and far more fierce when they put a helmet on and go out on their skates. I think the name can accommodate that."

Among others, the Dublin league features Scarlett McCabre, Feline Rowdy and Kim Makaze; their off-track professions range from teacher to PhD literature student, to wine importer, to homemaker with three children.

The rollergirls share an obvious solidarity. As much as they knock each other down, they pick each other back up. "I've never had so many good friends, all in one place, my whole life," says Kitty. "It's fantastic." Ailish agrees. "If you saw us outside, in our normal clothes, you wouldn't think this group of people would be together. But in here, everyone seems to click no matter what your background." She pauses. "You're beating lumps out of each other, but you're still appreciating each

"I'm going to be playing this when I'm 50," says Kitty. "Hobbling around with new knees. I love it." Derby takes over your life, one girl after another says and their pride in what they've made is plain. "We had a launch, a couple of months ago," Kitty continues. "And we did this thing where we had an MC who was calling out our derby names, and we had to skate up. And when they called out the first girl – Scarlett O'Harmer – I was just so happy and proud, I started to cry."