Roller Derby *acording to wiki*
So… How to explain Roller Derby to the generally derby deprived? Naturally, go to wiki! 😛
Roller derby is an American-invented contact sport—and historically, a form of sports entertainment—based on formation roller skating around an oval track, with points scored as certain players lap members of an opposing team. In past decades, roller derby had been primarily a professional or paid sport for both women and men. Contemporary roller derby is international, predominantly female, typically operates on an amateur (or unpaid) circuit, and has a strong do it yourself ethic  which often features both athleticism and a punk third-wave feminism aesthetic.
Roller derby takes place on a circuit track. Offense and defense are played simultaneously. The two teams playing send five players each onto the track — one jammer (scorer), three blockers (defense), one pivot (a blocker who may become the jammer later in that jam). Helmet covers are used to display the players’ positions: a cover with two stars is used for jammers, a striped cover is used for pivots and no cover is used for blockers.
Pivots and blockers from both teams start the game by forming a single pack. In a pack, all players face counterclockwise. The track has two lines marked across the track 30 feet apart, a pivot line and a jammer line around which the players build their initial formation.
Pivots line up on the pivot line and all blockers must line up behind them in any order they choose. The two jammers, who are not considered to be part of the pack, are positioned on the jammer line 30 feet behind the pivot line.
The referee signals the start of jam formation by blowing a whistle. During jam formation, the entire pack moves counterclockwise, during which time players can change position. All pivots/blockers must remain in the pack (i.e., no more than 20 feet in front of or behind the largest group containing blockers from both teams ). When the last person in the pack has passed where the front of the pack was initially lined up, the referee blows the whistle twice, signaling the jammers to take off, and play begins in earnest with a jam.
A jam is a 2-minute countdown period during which both teams attempt to score points. Points can only be scored by the jammers, who, moving counter-clockwise, 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 legally pass an opposing blocker/pivot. During a jam, all pivots/blockers must remain in the pack. Pivot/blockers attempt to assist their jammer through and out of the pack while simultaneously stopping the opposing jammer from exiting 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 rejoins to the pack.
The first jammer to legally pass all pivots and blockers once the jam begins wins the status of lead jammer for the remainder of the jam. The lead jammer can decide to end the jam at any time before the 2 minutes are up. She does this by placing her hands on her hips repeatedly, which signals the referee to officially call off the jam.
After a lead jammer has been established, both jammers have the option of passing their positions to their teams’ respective pivots (passing the star). This is done by removing the 2-star helmet cover and handing it to the pivot. The pivot then becomes the jammer, and the jammer becomes a blocker for the remainder of the jam. If the original jammer was the lead jammer, the position of lead jammer is not passed on; the position is forfeited for the remainder of the jam.
To impede the progress of the opposing team’s jammer, players may block using body parts above the mid-thigh, excluding forearms, hands, and head. Elbows may not be used in blocking, and cannot be swung at other players or used to hook an opponent’s or teammate’s arm.
Each game consists of two 30-minute periods. At the end of each jam, teams field another line up of players and the next jam starts exactly 30 seconds later.
Penalties are given to skaters who block illegally, fight or behave in an unsporting manner, or otherwise break the rules. Possible penalties include sending players to a penalty box (during which time opposing jammers score for opposing skaters in the penalty box when they score their first point in each pass) and expulsion of players. A skater goes to the penalty box for 1 minute immediately upon incurring a major penalty, or after accumulating 4 minor penalties.
In 2004, a number of all-female leagues formed what is now the Women’s Flat Track Derby Association (WFTDA), which coordinates and sets the rules that govern sanctioned inter-league competition among its members. The WFTDA member leagues create “travel” teams who play against each other in regional matches, although some leagues that are not WFTDA members have independently arranged their own travel teams and inter-league bouts. WFTDA also publishes rankings and organizes annual championship tournaments for its members in good standing. While not directly affiliated, many independent leagues around the world have adopted the WFTDA rules and standards either completely or as a foundation for their own rules.