Well, I could hazard a guess...
"Roll" is a common name for Ecstasy. "Rolling" is a term for using X. My son has often said "That person is so stupid, they rolled themselves into brain damage", meaning they've used too much X and now have permanent damage.
So, and again it's a guess, a "roller derby" could be some kind of party where X will be available. Maybe a rave, or some such?
Also, I've found several references to "skate sessions" that seem to imply when a group of skateboarders get together somewhere to skate (usually, some place they shouldn't be, like an office complex, parking garage, etc.) Since most of the "Sk8tr Boi's" I've run across with McWeedy were also drug fiends, the two could go hand in hand. "Roller Derby" could also go along with that skateboard theme, but that wouldn't necessarily mean drugs weren't also involved.
Not much, but it's all I could find on short notice.
Mikey