A Roller Derby team is organized into squads who take turns playing. Each game is called a bout, played in two 30 minute halves consisting of segments called jams that last up to 2 minutes in length and keep the action going. Within each team, the squads consists of: four blockers (with one as an optional pivot) and one jammer, who is only player to score points. "The pack" is a combination of blockers from both teams within certain distance of each other. Offense and defense are played at the same time by both teams simultaneously. The jam begins when the ref blows one short whistle.
The pack immediately begins to try to stop the opposing jammer while at same time helping their jammer get through. Whichever jammer gets through the pack first is deemed "lead jammer." The first time through the pack and the subsequent lap that follows is called the initial pass, and points are not scored. After skating around the track, the jammers try to get through the pack again, which is when they begin to earn points. Jammers score one point for each opposing blocker they pass at the hips (including those serving a penalty), as long as they pass that player while legally in bounds and without receiving any penalties.
So, what’s against the rules? Well, like any other sport, there are rules to keep players and referees safe. Roller Derby has TONS of detailed rules, penalties and strategies. You can read the entire rule book by clicking here. A skater can be penalized for a variety of things in several categories. They can be procedural or behavioral, and result in time being spent in the penalty box, or "Sin Bin". Earning 7 penalties in a single bout will cause ejection from the remainder of the bout, and extreme/certain situations can warrant ejection from the bout by the head ref no matter how many penalties a skater has. Examples of penalties include: Tripping, back blocking (pushing from behind), deliberately falling in front of another skater, using elbows for blocking or hitting, blocking or hitting more than 20 feet away from the pack (out of play), being insubordinate to a ref, unsportsmanlike conduct, and grabbing, holding or pulling an opposing skater.
Penalties are enforced by the refs that skate in the middle and outside of the track. These rules are for the safety of skaters and create a more dynamic game, so skaters have to use their strategic plays to get their jammer through the pack while stopping the other team!