Roller Derby is a full contact sport mainly played by women on old school quad skates. The game or “bout” is divided into two 30 minute periods and consists of 2 minute plays called “jams”. Each jam, two teams field up to four blockers and 1 jammer, numbers may decrease if penalties are being served. The “jammer” is the points scorer for her team and is identified by the star on her helmet. The four blockers for each team make up the “pack”. The blockers aim is to stop the opposition jammer from scoring while also helping their jammer to score points. One blocker is nominated the “pivot”, recognised by a striped helmet cover, this blocker has extra responsibilities like communicating or setting the pace of the pack.
To begin a jam, one whistle is blown which set the pack and jammers rolling. Both jammers race to get through the pack first. The first jammer out of the pack gains lead jammer status and has the advantage of being able to call off the jam before the two minutes has lapsed. Every lap of the pack after this initial lap, is scoring pass. Jammers score points by legally passing the opposition player’s hips and if they happen to lap the opposition jammer they gain her point as well.
If a skater does something illegal they we be waved off the track and must serve one minute in the penalty box.
More information and a brief history can be found here