The movie opens with Bliss Cavender (Ellen Page) participating in a beauty pageant. The contestants are lining up on stage and introducing themselves. Her mother Brooke Cavender (Marcia Gay Harden) is seated with the other parents since Bliss told her she didn't want her in back with her. The scenes with the mother with the other parents and the girls on stage are spliced with Bliss dying her hair with best friend Pash. When she is introduced to go on stage it is clear that her hair is a bright blue and her mother is not pleased.
Bliss is from Bodeen, Texas a small town in the mioddle of nowhere. She feels trapped in this town where she works with Pash at the local restaurant giving the local high school kids, "Squealers," huge sandwiches that if they finish in three minutes they get them for free.
While on a shopping trip with her mother in Austin, Bliss sees three roller derby girls enter the shop and roll up to the counter handing out flyers. She is immediately drawn to them and takes a flyer on her way out. Her friend Pash sees the flyer and suggests they drive to Austin.
Later that night at the roller derby they see the two teams compete, the Hurl Scouts (the team with Drew Barrymore) and the Holy Rollers. The Holy Rollers win as they are the best in the league and the Hurl Scouts are the worst. After the match, Bliss goes up to one of the rollers from the Hurl Scouts and tells them they are her new heroes and they tell her to be her own hero and try out for the team since they are having auditions. While Pash and Bliss are leaving the derby, Bliss locks eyes with a hot guy but shyly looks away.
Back in Bodeen, Pash tells Bliss that she will never have the guts to try out for the Hurl Scouts but Bliss does and she gets on a bus bound for Austin and tries out for the team. She is the fastest in the tryouts but is unable to really hit and be violent towards the other derby players. She is accepted onto the team because she lies and says she is 22 when she is actually 17. She lies to her parents and tells them she is doing SAT prep classes when in fact she is going to derby lessons.
Bliss realizes that while her mother thinks the only way for her to succeed is to compete in the beauty pageants Bliss is starting to love her new sport and is tired of mom shoving her beliefs down her throat.
They have their first match and lose but not before Bliss is thrown in late in the game and snags four points at once for the team. After the game they go to a house party where Bliss meets up with hot guy she had locked eyes with before, whose name is Oliver (Landon Pigg). He is in band with his brother. Oliver asks her what she is doing in five minutes and when she responds with, "No official plans," he tells her he'll be back. But then she is found by some of the rival players of the Holy Rollers one in particular the leader, Iron Maven (Juliette Lewis) seems to have an intense dislike and jealousy of Bliss and they throw her in the hot tub at the party. She goes into the bathroom to dry off and finds Pash making out with a random guy in the bathtub. Pash proceeds to get sick and Bliss instead of meeting up with Oliver takes care of her and they go home.
The next day Oliver shows up at Bliss's work because the previous night she had told him the name of the restaurant and town that she lived in. Pash covers for her and she spends the day with him where he takes her to the video arcade and then a field where he keeps throwing his car keys so as to spend more time with her.
The Hurl Scouts become better and better as they finally begin to have a drive to want to win and also start listening to their coach and his game plans and because of this they begin to win game after game. But trouble is just on the horizon. After a roller derby match that sends them to the championship match against the Holy Rollers the fire marshal and police come to shut it down due to size capacity. Pash gets caught holding a beer and is identified as a minor and arrested. Bliss is also identified as a minor but is told to go home. Iron Maven overhears this. Bliss leaves with Oliver after promising to find Pash but never does and doesn't know what happened to her. Oliver and Bliss go to a pool and have sex.
The next day Pash is pissed that her best friend ditched her and Bliss's parents found out about her roller derby secret. They yell and argue and Bliss leaves home. Through all this Oliver has left to travel with his band and Bliss calls him wanting to talk to him but gets no answer.
Bliss stays with one of her roller derby pals and she finally tells them she's seventeen after Iron Maven confronts her and insinuates that she will make it known. While staying with the roller derby friend she finds out she has a child and that is why she never hangs out after matches. The friend tells her to stop making it so hard for her parents and that her mom isn't that bad, she just cares about her.
Bliss goes to school and while there looks up Oliver's band online to see how their tour is going which is where she sees Oliver with his arm around some girl who is wearing Bliss's shirt that she has given him as a parting memento. She is heartbroken and goes home. Her mom comforts her and they have a heart to heart. Where they sort of begin to understand each other. Bliss decides to do the beauty pageant, which is on the same day as the roller derby championship. Her mother tells her to do the pageant for herself and not for her and Bliss says she's doing it for herself. But its clear that she's really doing it for her mother.
Pash and Bliss make up and Pash tells her that while Bliss was running away she had kissed Birdman and fellow friend who worked with them at the restaurant; someone who was really nice but who they had made fun of, a lot. Pash also tells her that she is going to Columbia University and is going to try living in New York for a while.
On the night of the roller derby and the beauty pageant, Bliss's father decides he would rather have his daughter happy and gives her parental permission to play since she is underage and picks up her roller derby teammates and takes them to the pageant to pick up Bliss.
There, the mother asks again if Bliss was doing this for herself or the mother and Bliss says she in fact was still doing this for the her, the mom storms out evidently angry and disappointed. Bliss's dad takes them to the tournament where she runs into Oliver who explains that the girl was just some groupie who had climbed into their van and had taken the shirt. She asks him why he didn't call and he says he was busy and she slaps him and says she would have called and she wants her shirt back.
At the championship match, Bliss's mom decides to come and watch and during the game Bliss is knocked down hard but still gets up and continues playing, echoing how her mother is also a fighter and never gives up. But the Holy Rollers still win but Bliss still wants to do this and move to Austin and stay on the team. The mother accepts this but acknowledges that it will be hard. The father is then seen hammering a sign into his front yard with his daughter's roller derby number on it, much like his neighbor does with his football sons.