I love Roller Derby
It's lots of fun!
Roller derby is a roller skating contact sport played by two teams of
fifteen members. Roller derby is played by approximately 1,250 amateur
leagues worldwide, mostly in the United States.
Game play consists of a series of short scrimmages (jams) in which both
teams designate a jammer (who uniquely wears a star on the helmet) and
four blockers to skate counter-clockwise around a track. 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