"I became completely and utterly addicted to roller derby," she said, though she couldn't maintain the three-night-a-week commute to Denver for the team's practices.
So in July 2011, MacArthur founded the Boulder County Bombers, a nonprofit roller derby league with an anti-bullying focus to get her roller derby fix.
Within the league are two teams, the Daisy Nukes and the Shrap Nellies, which have played each other twice this season. Each team has one win, so to the settle the rivalry, the Bombers are hosting one final bout-- the Night of the Living Derby Girl.
Proceeds from the bout will support Blue Sky Bridge, a Boulder child abuse prevention organization, which ties into the league's anti-bullying philanthropy efforts.
When MacArthur moved to Boulder two years ago, she knew that the community was "ripe" with interest in roller derby because of high attendance to see the Denver Roller Dolls, which often play at the 1stBank Center in Broomfield.
The Boulder County Bombers now practice in a Longmont warehouse -- the "Bomb shelter" -- where they provide intensive training for first-time skaters. There, newbies also learn the more violent aspects of the sport -- blocking, bumping, launching and hitting.
MacArthur recruited her friend Jordan "Lacy Vasive #C3J4" Honea, 25, to play for the league, even though she'd never skated competitively before.
"The first time I put on skates, I would just sort of hobble around and squeak if I got bumped," said Honea, an international studies and Italian student at the University of Colorado.
Now, she's the secretary for the league's board of directors, head of the events committee and blocker for the "A" travel team. She balances roller derby practice, which is often three times a week, with school and being a wife and mother.
Most women have little or no athletic experience before they took up skating, or it's been a while since they've played any type of competitive sport, Honea added, so she wasn't alone in her hobbling and squeaking.
Carly "Feist E. One #0815" Daelli swam in college, but said she's always getting her "butt kicked" in the rink by women who haven't played on any type of team in years.
"It's something anybody can do and it doesn't matter what size you are," said Daelli, a mother and neighborhood revitalization specialist for the City of Longmont. "If you're a tiny little woman, you can get through everyone fast. If you're bigger you can knock some girls down. There's a spot for everybody."
What MacArthur missed most when she stopped skating was the unique mix of women she found through at the rink. Women who are mothers and professionals, assertive or shy, big or small all find their way to the rink because something draws them there, she said.
"It's very intimate," said MacArthur, who traded a career as an analyst to own a derby apparel store, Deviant Derby. "The only other thing in my life that I have ever had come close to the roller derby community is church. You have this bond that is hard for others outside of the community to necessarily understand."
When Honea steps into her roller derby character "Lacy Vasive," she almost feels like a different person, becoming more assertive and less afraid to approach complete strangers.
"It becomes this obsession," Honea said. "You feel good physically and mentally and you have so many friends around you that it's something you don't want to miss out on."
--Follow Sarah Kuta on Twitter: @SarahKuta.
What: Boulder County Bombers Night of the Living Derby Girl
When: Saturday, Nov. 3, 7 p.m.
Where: St. Vrain Memorial Building, 700 Longs Peak Avenue, Longmont
More info: bouldercountybombers.com