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 whilst hindering the opposing jammer—in effect, playing both offense and defense simultaneously. Roller derby is played by approximately 1,250 amateur leagues worldwide, nearly half of them outside the U.S.
While the sport has its origins in the banked-track roller skating marathons of the 1930s, Leo Seltzer and Damon Runyon are credited with the basic evolution of the sport to its initial competitive form. Professional roller derby quickly became popular; in 1940 more than 5 million spectators watched in about 50 US cities. In the ensuing decades, however, it predominantly became a form of sports entertainment where the theatrical elements overshadowed the athleticism. This gratuitous showmanship largely ended with the sport's contemporary grassroots revival in the first decade of the 21st century. Although some sports entertainment qualities such as player pseudonyms and colorful uniforms were retained, scripted bouts with predetermined winners were abandoned.
Modern roller derby is an international sport dominated by all-female amateur teams, in addition to a growing number of male, co-ed, andjunior roller derby teams, and is as a roller sport under consideration for the 2020 Olympics. Most modern leagues (their back-office volunteers included) share a strong "do it yourself" ethic which combines athleticism and elements from punk, camp, and third-wave feminist aesthetics.