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.
The film sugarcoats Billie Jean King's love affair with Marilyn Barnett. In 1981, Barnett sued King, invoking "palimony" law, and nearly destroyed King's career. It took years for King to rebuild what she'd lost.
Bobby Riggs's hustling and male chauvinism were known prior to his match with Billie Jean King, but became more infamous afterward. In 1973, he guest starred as himself on The Odd Couple: The Pig Who Came to Dinner (1973), in which he hustled Oscar Madison out of everything, including his apartment lease and Felix. Riggs also gambled with Felix, betting that he would become a member of the male chauvinist club, Riggs' Pigs, if Felix lost. Billie Jean King also appeared in the episode.
The hair-cutting scene was deliberately tailored to invoke a sensation of so called ASMR - Autonomous Sensory Meridian Response. ASMR is a reported experience that people describe as a "tingling" sensation, typically beginning at the scalp. ASMR video and audio had grown as a phenomenon on home-produced media in the years before the film, and this inspired directors Valerie Faris and Jonathan Dayton. "People work to make videos that elicit this response" Jonathan Dayton said "and we were wondering: 'Could we get that response in a theatre full of people?'". The scene invokes several typical ASMR "triggers", such as: face closeups, soft-spoken voices, sounds of scissors and blow-dryers, personal attention.
The film only briefly touches upon the homophobic attitude of Margaret Court (the Australian tennis player). She correctly suspects Billie Jean 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.