Jen Hernandez -- better known to her teammates as "Mortisha Demolisha" -- suffered a concussion the first time she skated with a roller derby team.

She has seen teammates and opponents break wrists, fracture ribs and endure broken bones in their hands and feet. The carnage can get so bad, and is so much a part of the sport, that the MySpace page for Hernandez's team, the Escondido-based Hidden City Derby Girls, includes a photo gallery titled "Wall of Pain" that features snapshots of bruised elbows, banged up knees and shins with massive raspberries.

So why does Hernandez continue to participate in this rough -- not just around the edges but all the way through -- sport?

"I love the sisterhood," said Hernandez, 33, a forensic autopsy assistant for the county medical examiner (hence the nickname) who is also married with a 5-year-old son. "It's basically time for me outside of work and outside of my family.

"I love, of course, the athletic side of it. I played organized sports as a kid, and then I didn't do any of that for a long time. When roller derby fell into my lap, I was just in love."

After a few years with other teams, Hernandez started the Hidden City Derby Girls along with Amie Dewees (a florist nicknamed "Rosey Graves) and Rebecca Capps ("Becky Beerhouse") in August. The team is based at Ups N Downs skating rink on North Broadway in Escondido and was formed to give the women and others with similar interests the opportunity to participate in a sport that earned a cult following in the 1970s, one they say is experiencing a new boom in popularity.

The sport itself is somewhat more complicated than it may seem at first glance.

In a typical bout, two teams of five competitors each skate around a flat track -- usually about 1/16 of a mile around -- for two periods that are each 30 minutes in length (divided into two-minute segments). Each team has a jammer whose goal is to skate around the oval and navigate her way through the other team's blockers more times than the opposing team's jammer.

That, of course, is where the physical nature of the sport comes in, as the smaller, quicker jammers -- similar to wide receivers in football -- are hit hard by the blockers, who are essentially the linebackers, trying to keep them from getting through.

Jammers receive a point for every member of the opposing team that they pass on their laps around the track. A typical final score might be 117-110.

"You can't be scared of getting hurt," said Dewees, who doubles as the team's coach. "You can't be someone who's scared to try new things, and you definitely can't be somebody who isn't willing to get along with a bunch of (women)."

Those who may remember roller derby from the '70s and '80s can expect to a similar look from the modern version of the sport. The Hidden City Derby Girls' players skate on traditional four-wheel skates and wear knee and elbow pads, wrist guards, helmets and mouth guards. Their outfits consist of short shorts or skirts with knee-high socks and tank tops, and many of the skaters wear fishnet stockings, Dewees said, although that's more for protection against raspberries than for the look, she said.

For now, the Hidden City Derby Girls practice on Tuesday and Thursday nights, but they are working to schedule bouts with other teams. Their next scheduled event likely will be a scrimmage at Ups N Downs on May 5.

Watching the Derby Girls in action provides a good sense of just how rough and tumble the sport can be, and some may be surprised that it attracts skaters like Hernandez, a young professional with a family.

Carri-Lyn Cameron, a 26-year-old Escondido resident who goes by the nickname "Naughty Hottie" and serves as the team's de-facto public relations manager, said the team has about 20 members who range in age from about 20-40. She estimated that 25 percent of the team's skaters have kids.

Cameron played organized sports as a kid and has recently gotten into yachting, she said, but found roller derby a better fit with her waitressing schedule. It also suits her personality, she said.

"It's a great workout and a lot of fun," she said. "It's a great way to get out aggression. I'm pretty feisty, so it's a healthy way to express that."

Cameron said the team has regular monthly fundraisers and team events at various locations in Escondido and that its members aim to conduct themselves as respectable members of the community. The Derby Girls have had to let some skaters go -- they landed with rival clubs -- due to disciplinary issues, but team members said those were rare occurrences.

Still, they make no bones about their toughness -- their official team logo features the slogan "We Maim To Please."

"It's girls with a lot of energy and spunk who aren't afraid of getting dirty and sweaty and getting knocked around a bit," Cameron said of her teammates, laughing. "They're all cool, but you wouldn't want to mess with them if you didn't have to."