She said, "It was such a thing to figure out how her hands moved and the way she moves within her body. I was a real creep. So now if we do an interview or we're sitting and talking, I find myself staring at her and watching how she's moving all the time, which I don't need to do any more. But that's how I relate to her. I'm like her creepy friend now!"
The actress also shared that she steeped herself in vintage TV footage to get into the skin of the role.
Stone explained, "We quickly learned that the choreography would be the most important thing because learning how to do a serve or backhand like Billie Jean was more of an impossible dream than a reality! I really thought through the physicality. There was a lot of bulking up, tennis lessons, learning her stance and feeling my way into her body. She is a machine."
The movie offered a chance to Stone to know King personally, but the 'La La Land' star was a bit reluctant about that.
"I didn't talk to her too much while filming because it was too much pressure. And she has all the benefit of hindsight of decades older now," noted Stone.
The film's plot is loosely based on the 1973 tennis match; when Riggs challenged King for a faceoff.
'Battle of the Sexes' became the most-watched sporting event of all time.