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 worldwide. 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.
Contributions by Mjb, Marumari, and 188.8.131.52.