Roller derby leagues have slight rule variations, but here is a look at rules used by the Texas Rollergirls league in Austin:
* Teams may have more than a dozen players, but only five can take to the rink at a time during competition between two teams -- a pivot, a jammer and three blockers.
* Skaters jockey for position and ram into each other during four 14-minute periods. They race around the track as each team propels its jammer, a player who scores points by passing opponents.
* The pivot wears a striped helmet and skates at the front of the pack, setting the pace while trying to help her jammer.
* Blockers work to block the opponent's jammer and to create passageways for their jammer.
* Jammers start at the back of the pack and can score points during "jams" that last as long as two minutes. After jammers lap the pack, they get one point for each opponent passed. The first jammer to break through the pack is called the lead jammer. She may call off the jam by putting her hands on her hips.
* Players can be penalized for improper blocking, grabbing, holding, deliberately falling in front of another skater, intentionally cutting through the middle of the track, fighting, intentional roughness and "gross unsports-girl-like conduct."
* If the score is tied at the end of the fourth period, the game goes into five-minute "sudden death" periods until a point is scored.
-- Associated Press