When most sports leagues talk about growth, they're usually referring to higher salaries or bigger, better stadiums.

For the Minnesota RollerGirls, though, it's the sport itself - roller derby - that has grown noticeably in popularity, organization and the collective skills of its players.

And it's all happened in the lifespan of a toddler.

"Roller derby is continually growing, both nationally and internationally. I hear about a new league about once a week," said Mary Donnelly, a rollergirl also known as Head Trauma.

Donnelly is responsible for bringing female roller derby back to Minnesota, after reading an article about the phenomenon and taking a road trip to Texas to see a bout firsthand. In December 2004, the Minnesota RollerGirls held their first bouts at Cheap Skate roller rink in Coon Rapids. In 2005, they upgraded to Roy Wilkins Auditorium in St. Paul.

Donnelly said that, in addition to the increasing popularity, the sport itself is changing. "When we first started and even when the sport was started, roller derby was definitely more spectator," she said. "It surprises me how much it has evolved."

While much of this growth has happened organically, the sport has also grown because of deliberate attempts to organize a national network. Today 34 leagues belong to the Women's Flat Track Derby Association, including the Minnesota RollerGirls. A local independent league, the North Star Roller Girls, now holds bouts at Cheap Skate.

Minnesota head coach and head referee Denny Royal, a k a Rat Bastard, agreed that the sport is progressing, but emphasized the growth he sees in players' skills. "[Roller derby] continues to get more athletic. It's rougher, with faster, bigger hits. It's not as campy as when we started out," he said.

All of which means that, as the RollerGirls begin their third home season Saturday at Roy Wilkins, fans probably will see faster skating, better strategizing and more all-around aggressive competition than in previous years. And, for the fans who love nothing more than to see a rollergirl wipe out or bleed, this could translate to more players in pain.

"There are real injuries, and the injuries are usually pretty bad," Rat Bastard said.

Anyone planning to attend a derby bout for the first time this weekend can be sure of one thing: The winners will all be Minnesota RollerGirls.

During the home season, the 80 Minnesota RollerGirls break into four teams that compete against one another. On Saturday, the Dagger Dolls will play the Rockits in the first bout, and the Atomic Bombshells will face the Garda Belts in the second.

The home season looks to be more fan-friendly than last fall's interleague season, in which a select group of Minnesota RollerGirls faced other WFTDA teams. "At home team bouts, there are a lot more friends and family there," said Rat Bastard. "It's your favorite team playing, not just the home team."

Fans cheering for their favorite team will get a little help from the "Superfans," four pseudo-cheerleaders who dress up in team colors and paint their faces, along with team mascots. "People love the Rockits because of [star jammer] Jawbreaker, but the Dagger Dolls have the craziest fans," said Donnelly.

This season, though, fans might have to reassess just which team they are cheering for, because last year's stronger teams could easily change. The Garda Belts, a powerful team last year, have added 10 rookies -- and the last-place Atomic Bombshells have recruited four of the best skaters from other teams.

So, which teams are this year's likely frontrunners?

Rat Bastard insisted that the teams are quite well matched, and that he has no idea who the best team is.

"It changes every year, who the hot-shot team is," he said. "We'll find out on the 27th, won't we?"

Despite derby's ballooning notoriety and increased skill levels, the basic tenets of the sport, and the RollerGirls' reality, have changed little. Players receive no salary, and all proceeds from team bouts and events go to the league or to charity.

Being a rollergirl is a massive time commitment, too -- especially because most players have full-time jobs. Dagger Doll and third-year RollerGirl Leah Colvin Roy, 31, a k a Lydia Punch, said the amount of time the sport takes up can be challenging.

"It's supposed to be a hobby," Punch said. "It's stressful and consuming at times." But, "a lot of people consider derby a lifestyle," she added.

The lifestyle aspect, for the most part, seems to be a reality that many rollergirls embrace, noting the many positive aspects of the sport and the effect it has on their lives.

"We do this because we love to skate, we love the relationships we get to have with other women and we love the contact-sport and team aspects," said Dagger Dolls rookie Cynthia French, 33, a k a Dottie Hazzard. She tried out because derby is "cool, fun, great exercise, run by skaters and accessible."

Referee Rat Bastard, a former quad speed skater, roller hockey player and Army Ranger, is just as enthusiastic.

"It's a phenomenal sport, and it's fun to be a part of it."

Roller Derby season openers: Dagger Dolls vs. Rockits; Atomic Bombshells vs. Garda Belts.