"I didn't play at all beforehand but I played sports in high school and in college and it was really important to get the tennis right," he tells "Good Morning America", "so I was really grateful I got to train at a place called the Wheel Tennis Academy in Ojai, California, where I live."
"It had unbelievable coaches and I trained not only in playing tennis, but also they let me coach. I got to coach this top 50 junior nationalist, Kamea Medora. I got to train her, run drills, get into the vocabulary of coaching... and I'm really grateful for that." He added with a smile, "I think we got the tennis right."
In a separate interview, Bernthal talked about what drew him to the movie. "As a father, and as an ex-athlete, I just thought the script was so nuanced," he told ScreenRant. "It just centered on this sort of age-old struggle, which is: how do you raise your kids?"
"We love our kids so much, but how do we make these right decisions? Sometimes when you love them so much, do you love them too much? And when do these right decisions start to fall over on the wrong decisions? I fell in love with the script."
"And then I think with Rick Macci, specifically, he just was such a lover of the game. Everyone who played there talked about it just being so fun there, and how it was always a game. I really wanted to try to capture that, and I'm so grateful to those wonderful, special coaches that I've had in my life - and the ones that have coached my kids."