In 1973, Billie Jean King was 29 and Bobby Riggs was 55. At the time of filming, Emma Stone was 28 and Steve Carell was 54.
Emma Stone was initially cast as Billie Jean King, but scheduling issues forced her to pass on the role. Brie Larson was ultimately tapped to replace her. After a few months, Larson dropped out. After Stone's schedule was cleared, she was able to take back the role.
While riding in the car, Billie Jean King and Marilyn Barnett listen to an Elton John song. John, a friend of King's, wrote his hit single "Philadelphia Freedom" in honor of her.
The film only briefly touches upon the homophobic attitude of Australian tennis player Margaret Court. She correctly suspects Billie Jean King is having a lesbian relationship with her hairdresser, and speaks of "immorality" and "sin". In real life, it went further; Court became an anti-gay activist after her tennis career, vocally opposing same-sex marriage in Australia.