Karen wants more action out of life and quits her job at the cannery to become a skater in the roller derby. She encounters friction from the other skaters - especially Mickey, the current number one star of the team. Karen proves herself a feisty competitor but refuses to be a team player. As she skates her way to roller stardom, she incurs the wrath of jealous team members and the owner of the team.

Karen Walker, a production line worker at a cat food factory, quits her job when the foreman sexually harasses her. After speeding up the automated conveyor belt so that it hurls cans across the factory's floor, the scrappy Karen shoves some cans in the foreman's face then walks out. Still exhilarated from watching a roller derby game the previous night, Karen decides to try out for the Los Angeles Avenger Roller Derby team. Recognizing that Karen's spunk and good looks will be a hit with the crowds, Stern, the owner of the team, hires her. On her first night as the Avengers face off with their arch-rivals, the San Diego Demons, Karen is propositioned by Mickey Martinez, a lesbian who is the Avenger's highest scoring player. When one of the Avengers is sidelined by an injury, the team's whip-wielding coach, Angie Striker, sends Karen in to take her place. Rather than follow the game plan as instructed however, Karen shows off by knocking down Demon Masked Marvin and snatching off his mask. After the game, Karen joins the rest of the team for a drink at a bar where Mickey, Jennifer and several other Avengers criticize her for not following the choreographed routine, and as punishment, push her onto a pool table and rip off her clothes. Nick, the only member of the team who comes to Karen's defense, retrieves her clothes and offers her a ride home on his motorcycle. Later that night they return to the roller rink, where they strap on their skates and ram into each other on the rink before having sex. The next day, Karen introduces Nick to her roommate Donna and Donna's boyfriend Greg. The four drive off together, and at the end of the day, Karen decides to have the name "Avengers" tattooed onto her arm. The Avengers then travel to San Diego to meet the Demons. When Karen once again slams Masked Marvin and raises her tattooed arm in a victory salute, the crowd roars its approval. Later on the team bus, Nick surprises Karen by revealing that he is married and introducing her to his wife. Undeterred, Karen carries on her passionate affair with Nick. Buoyed by her popularity, Karen is hired to appear in commercials and soon finds herself earning enough money to buy a house and fancy new car. In a match with the Demons, Karen is within three points of breaking Mickey's record when Mickey deliberately plows into her. When Rocco from the Demons joins Mickey to pummel Karen, a free-for-all erupts which results in Mickey being traded to the Demons for insubordination. Karen is then promoted to be the Avengers number one player, the player allowed to wear the helmet and score points. In need of a number two player, Stern imports Beverly Brayton from Fresno because she is black. Karen's success has made her even more cocky, and when Stern criticizes her attitude, she insults his manhood and kicks him in the groin. Soon after, Donna and Greg depart for Oregon to open a topless motorcycle repair shop. As time passes, the crowd warms to Beverly, making Karen even more belligerent and competitive. In a match between the Avengers and the Demons, Karen and Mickey start a fight, and the judges order a grudge race between the two players to resolve it. During the race, Karen shoves Mickey out of the ring, causing her to strike her head against the bleachers. Gravely injured, Mickey is hospitalized, angering the Avengers. To retaliate, the team gang up on Karen in the parking lot, and after beating her up, scratch her new car. Furious, Karen rams her car into one of her assailant's vehicles, then recklessly speeds off to visit her drunken, slatternly mother. That night, Karen is late to the game, and in her absence, Beverly has won several points as the lead player. Taking the helmet from Beverly, Karen enters the ring determined to best her rival. However, when Jennifer deliberately knocks down Karen, the Demons jump on her and the Avengers refuse to come to her aid. In a rage, Karen slams Beverly with the helmet, then goes berserk and skates off the track and out of the door into the parking lot. As she weaves crazily through the lot, Karen plays tag with the cars, slamming into them until one knocks her down. Still defiant, Karen picks herself up and raises her arm in a victory salute.