The sport of roller derby serves as the central motif of Roller Girl and is used as a characterization tool and plot device, which propels Astrid to grow and learn from her mistakes. It also leads her to meet her new friend Zoey after losing Nicole. Astrid sees a roller derby game with Nicole and her mother one evening at the beginning of summer and thinks it is “a lot better than the art museum” (14). She describes the people as strange-looking, and it feels like a whole new culture for Astrid. Astrid thinks that the roller girls “all looked really tough” (15) and have cool names. She soon signs up for roller derby camp and believes that Nicole will too. Instead, Nicole signs up for dance camp, leaving Astrid to go to derby camp alone. Astrid is determined to become like her favorite roller girl Rainbow Bite and attends the camp without Nicole (although begrudgingly). Astrid finds it very intimidating at first since all the girls appear much older and more skilled, but this changes as Astrid persists and develops confidence.

At roller derby camp, Astrid learns how to skate, hit, block, stop, and fall.