Roller derby takes place on an oval track, with two teams sending five players each onto the track — three blockers (defense), one pivot (last line of defense) and one jammer (scorer). Helmet covers are used to display the players' positions: a striped cover is used for pivots, a cover with two stars is used for jammers, and no cover is used for blockers.

Pivots and blockers from both teams start the game by forming a single pack. The two jammers, who are not considered to be part of the pack, are positioned 20 feet behind on the start line. The referee signals the start of jam formation by blowing a whistle. On this first whistle, the blockers begin moving counterclockwise around the track. Once the last blocker in the pack has passed where the front of the pack was initially lined up, the referee blows the whistle again, and the jam begins!

A jam is a 2-minute countdown period during which teams attempt to score points. Points can only be scored by the jammers who attempt to pass the pack and lap around as many times as possible. After passing the pack the first time, jammers earn one point each time they pass an opposing blocker/pivot. During a jam, all pivots/blockers must remain in the pack. If a pivot/blocker falls or otherwise becomes separated from the pack, she is out of play (i.e., cannot block or assist the jammers) until she catches up to the pack.

The first jammer to pass all pivots and blockers cleanly once the jam begins wins the status of lead jammer for the remainder of the jam. The lead jammer controls the play and can end the jam at any time before the 2 minutes are up by placing her hands on her hips, signaling the referee to officially call off the jam. To impede the progress of the opposing team's jammer, players may block using body parts above the hips, excluding hands and head. Penalties are given to skaters who block illegally (elbow, trip, clothes-line, grab, pull skaters down), fight or behave in an unsportsmanlike manner, or otherwise break the rules.

Roller Derby Explained: Online Video