page_title: Roller derby
section_title: Jams
hierarchical_section_title: Roller derby / Rules / Jams
caption_attribution_description: English: Two roller derby jammers (of the Rainy City Rollers and Chica Chula of the Oly Rollers, respectively) at their starting position.
context_page_description: Roller derby is a roller skating contact sport played by two teams of fifteen members. Roller derby is played by approximately 1,250 amateur leagues worldwide, mostly inside the United States.
  Game play consists of a series of short scrimmages in which both teams designate a jammer and four blockers to skate counter-clockwise around a track. The jammer scores points by lapping members of the opposing team. The teams attempt to hinder the opposing jammer while assisting their own jammer—in effect, playing both offense and defense simultaneously.
context_section_description: Play begins by blockers lining up on the track anywhere between the "jammer line" and the "pivot line" 30 feet in front. The jammers start behind the jammer line. Jams begin on a single short whistle blast, upon which both jammers and blockers may begin engaging immediately.
  The pack is the largest single group of blockers containing members of both teams skating in proximity, arranged such that each player is within 10 feet of the next. Blockers must maintain the pack, but can skate freely within 20 feet behind and ahead of  it, an area known as the "engagement zone".
  The first jammer to break through the pack earns the status of "lead jammer". A designated referee blows the whistle twice, and skates near, and points at, the lead jammer. Once earned, lead jammer status cannot be transferred to other skaters, but certain actions (notably, being sent to the penalty box) can cause it to be lost. The lead jammer can stop the jam at any time by repeatedly placing both hands on their hips. If the jam is not stopped early, it ends after two minutes. If time remains in the period, teams then have 30 seconds to get on the track and line up for the next jam. If the period expires, it does not halt a jam that is underway.
caption: Two jammers (from the Oly Rollers and Rainy City) race from the jammer line
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