Roller derby is a contact sport played by two teams of fifteen members roller skating counter-clockwise around a track. Roller derby is played by approximately 1,250 amateur leagues worldwide, mostly inside the United States. The gameplay consists of a series of short scrimmages (jams) in which both teams designate a jammer (who wears a unique designation on the helmet; currently a star) and four blockers. The jammer scores points by lapping members of the opposing team. The teams attempt to hinder the opposing jammer while assisting their own jammer—in effect, playing both offense and defense simultaneously.
Jams
Play begins by blockers lining up on the track anywhere between the “jammer line” and the “pivot line” 30 feet in front. The jammers start behind the jammer line.[1]:12 Jams begin on a single short whistle blast, upon which both jammers and blockers may begin engaging immediately.
Blocking
A skater may block an opponent to impede their movement or to force them out of bounds. The blocker must be upright, skating counterclockwise, in bounds, and within the engagement zone. Blocking with hands, elbows, head, and feet is prohibited, as is contact above the shoulders or below mid-thigh, and blocking from behind.
