The 1961 T-Bird's rivals, The Cycle Lords
The Cycle Lords were a gang of motorcycle hoodlums and degenerates who cruised around the city (Norwalk, CA), and generally lived to torment and harass the T-Birds.
They were led by Leo Balmudo, former leader of the defunct Scorpions. As Balmudo lost the Thunder Road `Racing For Pinks' (Pink slips, ownership papers) challenge to Danny Zuko, Balmudo had lost his car, assumedly Danny Zuko gave Balmudo's car to Kenickie, and kept the newly modified Greased Lightning.
Balmudo took up motorcycles and formed this new group of hoods, perhaps some holdover members from the Scorpions. Balmudo's right-hand man was Freddie (Cycle Lord), played by Freddie Hice. It can be assumed that after losing the Thunder Road challenge, Cha-Cha and Balmudo broke up, her disgusted that her man had lost his car to Leo Balmudo.