What is roller derby? Roller derby consists of two teams of five skaters each on the track. Each team has one scoring player called a jammer, who starts at the back and wears a star on her helmet. The rest of the skaters are called blockers, and they form a pack. The blockers get a head start on the jammers when the first whistle is blown; the jammers start sprinting at the sound of the second whistle. The jammers have to get through the pack and back around another lap before they can start scoring. On their second and future trips through, they get a point for every opponent they pass. Everyone else tries to stop the other teams' jammer from passing while helping their own jammer through. The team with the most points at the end of the bout wins.