Back in the 1960s, there were two main competing groups (kinda-sorta of like the American and National leagues of baseball).  One trademarked the name Roller Derby, so the other used Roller Games.  As I understand it, the Rules were basically the same.  (I'd be curious what the differences were if anyone knows that level of detail.)  The Thunderbirds, or T-Birds as they were sometimes known, were one of the teams that made up Roller Games.