Roller derby was born on Aug. 13, 1935, at the Chicago Coliseum. The story goes that Leo Seltzer, an event promoter who had cut his teeth on walkathons, was looking for something a little more exciting to draw Depression-era crowds. After reading in a magazine that more than 90 percent of Americans had roller-skated at some point in their lives, he decided to put his show on wheels.

Twenty-thousand people came out for the first Transcontinental Derby to watch two-person teams, each consisting of a man and a woman, skate 57,000 laps around a flat track, Keith Coppage writes in “Roller Derby to RollerJam: The Authorized Story of an Unauthorized Sport.” Small lights on a large map tracked the skaters’ progress as they took turns whizzing around the ring, their mileage blinking along the route from New York to San Diego. The first team to complete the roughly 2,700 miles from coast to coast was declared the winner. On average, a single marathon took more than three weeks.

Worried that the endless laps were getting, well, repetitive, in 1937 Seltzer turned to the sportswriter Damon Runyon. Together, they created what would become the enduring structure of roller derby and introduced the full-contact thrills that define the sport today.

In each bout, as a roller derby match is called, 10 skaters at a time take to the track. There are five players from each team: one jammer, whose job is to lap the other team and score points, and four blockers, who try to stop the other team’s jammer and clear a path for their own. At the start of each round, known as a jam, the two jammers race to get out of the pack first. Whoever prevails becomes the lead jammer. The jam then goes for two minutes, with teams earning a point every time their jammer laps a member of the opposing team. The lead jammer can also end a jam early by tapping her hands repeatedly on her hips.

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- History of Roller Derby, excerpted from Jennifer Harlan's 2019 NYT piece, "The Long and Surprising History of Roller Derby"

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