Final answer:
In 'Roller Girl,' the jammer is identified by the star on their helmet, and it's their role to score points by lapping the opposing team's members.
Step-by-step explanation:
In the book Roller Girl, the jammer can be identified as the player wearing a star on their helmet. The goal of a roller derby game is for the jammer to lap members of the opposing team to score points. While the jammers aim to race ahead, other team members, known as blockers, work to protect their jammer and hinder the opposing team's jammer.