Yeah, so Derby eventually evolved into professional wrestling on wheels by the early 80s. It was reborn as a female only sport around 2006 and eventually spread. Whip-It came out in 2009 and brought a ton of people to the sport. Banked tracks are complicated and expensive so it became flat track. At first it was female only, but because it was very progressive and punk, they were very accepting of various genders, so the rule was you could play as long as you didn't identify as cis male.

Men's derby started becoming a thing, and to fill out teams women skated with the men. The rules are the same, but they tend to hit harder. Most men's teams have a few women, who have no problem competing. Skating ability is more important then physical size and strength.

So as of now, except for the top teams it's more or less co-ed. It's hard to field a team that is gender segregated.

If you have a team that plays in your area it's worth it to go check it out.