Skating fast on the flat track, "Ida Kildher," co-captain of the North Star Roller Girls' Violent Femmes, doesn't really try to carry out the threat her name implies.

Still, she's more than ready to mix it up in classic roller derby style, knocking opponents around and getting knocked around — that's largely why she, her teammates, the other team and the fans the Minneapolis Convention Center are there.

The one who bears the brunt of Kildher's punishment the most may well be her alter ego, Nicole Rubis, the soft-spoken Columbia Heights high school and fifth-grade band teacher who has portrayed her for five seasons.

"Sometimes if I'm more on the sore side, conducting might be a little more challenging," Rubis said. "But I just go with it. The kids might be like, 'How'd it go? Did you win?'"

Rubis kept quiet about her skating during her first season with the Violent Femmes. A couple of seniors figured something was up, however, when they noticed her coming to school sore and bruised.

The word got out officially when the school paper did a story on teachers' lives outside of school. Students, who have come to her bouts, teachers and parents all have been supportive, she said.

Rubis made the Femmes after going to the North Star Roller Girls' tryouts in 2006. A friend on her kickball team who also was playing derby had talked her into seeing one of her bouts.

In a nutshell, I tell people you get to see girls on skates knocking each other around. It's not really the point but that seems to be the draw.

I've been really fortunate not to be injured from derby. I've seen broken ankles, broken legs, broken wrists, separated shoulders, concussions. My legs are covered in bruises. That's about as bad as it's gotten for me.

One of my former students skates with us now. When we played her team, it was one of my goals, being way older, to jam against her and beat her. There are little things like that but nothing where we want to kill each other.

I'm not very creative. We were at the bar after practice one night and another skater said, "Do you have a name yet?" I said no. She said, "I thought about this one (Ida Kildher) but didn't use it so if you want it it's yours."

It depends on the game and how physical it gets. Typically it kind of feels like you were hit by a truck the next day.