"I could smell the rubber on my soles burning, from skidding myself to a stop."
It was the difference between playing to the back rows, and playing it quiet, tamped-down, to allow the scrutiny of a camera lens.
"I guess it's Clint's realistic pace," he explains. "It's a much different experience, a much more real experience - in terms of psychological reality and psychological insight."
Young, who turns 39 on the Fourth of July, won the role of Valli in the original Broadway musical, which opened in November 2005. Then he took home Tony, Drama Desk, Outer Critics Circle, and Theatre World awards for his performance. After two years of playing Valli - whose vocals carried "Sherry," "Walk Like a Man," "Rag Doll," "Let's Hang On," and an amazing succession of tunes up the Top 40 charts - he ceded the part to other actors who could approximate Valli's alpine song stylings. Young was invited back to the August Wilson Theater for a reprise in late 2012 and early 2013.
"And that's when Clint saw me," Young recalls. "He was going around to the different companies of the show . . . getting a sense of this story that he was about to direct."
Although at first glance it seems an unlikely project for Eastwood, the icon of American stoicism - and the guy who famously talked to an empty chair at the 2012 Republican National Convention - grew up in a family of musicians. He directed Bird, about jazz great Charlie Parker, and has composed the scores for seven of his own films.
When Jon Favreau fell out as the director attached during development, Eastwood tossed his cap into the ring.
Then he showed up at the Jersey Boys Sunday matinee.
"Lo and behold, we heard the audience giving a standing ovation to him as he entered the auditorium, and, after the show, I met him backstage, and he and I shared some words . . . . And I said goodbye.
"And the next time I saw him was on his set, cast in his movie. That was my audition!"
A brief chat - and a front-and-center performance for Eastwood to consider. "It was the easiest, and yet the most impactful, audition of my entire career," Young marvels.
In Eastwood's Jersey Boys, opening Friday, Young's Valli is a gritty city kid, an Italian American who came up jostling with mobsters and thugs ( Christopher Walken is Gyp DeCarlo, the local crime boss). Valli and his band - including songwriter and keyboardist Bob Gaudio, played by Jersey Boys national touring company veteran Erich Bergen - face obstacles of their own making, and more typical music biz roadblocks. With its marital and money woes, the movie, even more so than the stage show, is a tale of struggle, of setbacks. It is also a tale buoyed by a truly remarkable collection of songs.
Getting to know the real Valli - and playing him onstage, and now onscreen - was another challenge for Young, who was born in Sacramento, lived in way-Upstate New York, and attended Brown University.
"At first, it was a little uneasy," Young says of his relationship with the pop idol, now 80, and still out there concertizing from time to time. That was "only because he was a little uneasy with serving his life up for public consumption in the way that Jersey Boys did. And I was right in the line of fire of that uneasiness, since I was the one cast as him. It wasn't personal, but it was weird."
Young says Valli found the idea of watching someone reenacting his life spooky. At the same time, Young knew he had to honor Valli and the book written by Marshall Brickman and Rick Elice.
"It's not necessarily true to every detail of Frankie's life as though it were a documentary, but true to the show, which was an entertainment based on his story," Young says. "And that was tricky, because I had to say to myself that it can't matter what Frankie wants this to be. I have to do what I've been hired to do.
"But over the years, I think he has become more comfortable with the fact that his life has been out there, depicted by, now, a lot of guys. And Frankie's an executive producer on the movie, so, clearly, I wouldn't have played the role on film if he didn't approve."
Young, who has a new album, My Turn, released on iTunes and Amazon ("it's me as me, not as Frankie Valli"), says one of the things Eastwood did in the film was to dig deeper into the contrast between Valli and his bandmates' messy backstories and the pristine pop music they made.
"What's even more salient in this movie as compared to the stage show is that it comes much more to the forefront that there's this story about these guys from this really rough side of the neighborhood, and it's almost uncanny that these songs came from these guys in these situations. That their songwriting, and their songs, were so great, and their personal lives were so troubled and so tumultuous. And not what you would expect.
"Except in certain instances," he adds, "like the song 'Dawn,' which has Jersey written all over it. Think about it: It's a working-class guy who wants to break up with his girlfriend, and instead of doing it directly, he just says, 'I'm not good enough for you, you need to find a better guy.' I mean, how manipulative and Jersey is that?"