Here is a concise history of women's roller derby. Although the roller skating craze dates to the turn of the 20th century and lasted through the Jazz Age, the combative, EXTREME sport version dates to the mid-'30s. Its popularity grew through the '40s and early '50s, when it was broadcast on TV. In 1940 there were 5 million spectators, or nearly 4% of the entire US population at the time, as if there were 11 million fans today.
Some pictures from its mid-century heyday:
Perhaps by the late '50s, and no later than the '60s, it began losing popularity, only used for pure camp value in the '70s, and absent from the '80s and early '90s. Only in the late '90s did interest re-emerge, and its 21st century revival is another example of how the Millennial age is repeating so much of the mid-century culture.
The only thing that distinguishes these periods is the trend in the crime rate. During rising-crime times, voyeuristic fascination with other people's pain and failures disappears. People actually participate more in sports, especially in team settings, but it's more to let loose their ambitious drive, act as a member of a larger team, and feel socially integrated into the larger community.
During falling-crime times, everyday violence isn't so common, so people try to over-stimulate themselves with violent imagery to make up for it. Human beings just have a certain need to see violence in their cultural products. But because people are more cocooning and emotionally unattached to their peers, this takes on a more lurid and voyeuristic quality. Unwholesome. If there had been YouTube in the mid-century, it would have been full of "fail" videos. (But not if they'd had it in the '80s.)
Seeing the roller derby gals from the mid-century knock into and tumble helplessly under each other was part of a broader voyeurism about violent women and girl fights. The heartless femme fatale was a stock character from film noir movies of the time (not only the better ones, but the cheesy ones too). And mid-century comic books, akin to today's video games, regularly featured images of voluptuous dominatrices, butt-kicking babes, and girl fights. Below are just three covers out of many on the theme, with the middle one coming from an entire series devoted to Crimes By Women.
Apart from the demand-side effect of greater voyeurism in the mid-century and Millenial periods, what about the women who star in the show? In falling-crime times, women just seem more snippy and cutting toward one another, and toward men as well, beyond the female animal's basic bitchiness. You don't see it in action as much because they're more cocooning in those periods, but things like femme fatales and roller derby reveal how they behave when they do lock themselves in more competitive settings.
It wasn't like the craze for women's tennis and golf in the Jazz Age or the New Wave Age, where they emphasized sportsmanship and the fun-loving aspects of competition.