Q: Is the action real? I thought roller derby was fake, kinda like pro wrestling.
The short answer: It's not fake any more. Unlike the derby of the 70s or pro wrestling of today, modern roller derby is a completely legitimate, competitive sport.
The long answer: From its invention in the 1930s up through the 1950s and later, classic roller derby was a basically legit and very popular sport. Through the 60s and into the 70s, theatricality and predetermined outcomes became more prevalent.
By its demise in 1973, classic roller derby had fully embraced the pro wrestling philosophy of spectacle over sport, and most people today retain a vague memory of the sport in that state. Ill-fated revivals attempts in the 80's and 90's went even further down the rabbit hole, culminating in RollerJam [1]'s figure-8 track and alligator pit.
When roller derby was reinvented in Austin, Texas, starting in 2001, those same recollections of the old spectacle and fakery definitely informed the derby girls' original intent. As they trained up, though, they came to discover that the best way to make a knockdown look convincing was to actually knock the other skater down, and before long they'd dropped the choreography entirely in favor of real contact with consistent and enforced rules.