Roller derby rose to prominence with televised coverage in the US in the 1940s.
That's how they rolled
Roller derby grew out of a US trend for roller-skating marathons on banked tracks in the 1930s.
It achieved mass popularity when it was first televised in the US in the 1940s. From the 1950s to the 1970s, there were travelling teams, attracting spectators with regular fights, spills and injuries.
The uniforms changed with the times, becoming progressively more revealing. The violence on the track also increased and Hollywood glamorised the sport in the film Kansas City Bomber.
But by the 1980s, roller derby was losing its mass appeal and became no longer profitable, despite promoters' attempts to increase excitement with more staged fights and laser shows.
There were several unsuccessful attempts to revive the sport at the end of the century.
In early 2000, the Women's Flat Track Derby Association was formed and roller derby began a new era.
The leagues were run by the athletes and formed as businesses. Instead of banked tracks, players used basketball courts or skating rinks - anywhere there was spectator seating.
Hollywood revisited the sport in 2009 when Drew Barrymore directed and starred in Whip It.
The sport spread to Europe, South America and Australia, and by 2010 there were more than 450 flat track roller derby leagues worldwide.
The inaugural Roller Derby World Cup was held in Canada last year with 13 countries represented. Each had a roster of 20 skaters.