Roller derby is an American-invented contact sport—and historically, a form of sports entertainment—based on formation roller skating around an oval track. In past decades, roller derby had been primarily a professional or paid sport for both women and men. Contemporary roller derby is international, predominantly female, typically operates on an amateur (or unpaid) circuit, and has a strong do it yourself ethic which often features both athleticism and a satirical punk third-wave feminism aesthetic.
Here is roller derby explained, in a bizarre animated style: