Roller derby is a contact sport played by two teams of five members roller skating in the same direction around a track. Game play consists of a series of short matchups ("jams") in which both teams designate a scoring player (the "jammer") who scores points by lapping members of the opposing team. The teams attempt to assist their own jammer while hindering the opposing jammer in effect, playing both offense and defense simultaneously. Roller derby is played by more than 1,200 amateur leagues on every inhabited continent.
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