"So, he says, 'I just want to know if you want to play Jackie Robinson,' and I said, 'What do you mean?' "
Boseman thought it was some tough-love pep talk - if you really want to play Jackie, you have to up your game.
"I thought he was leading me to something else, telling me you've got to play it better than what you did."
But in Helgeland's eyes, there was nobody better. Boseman had the right look, he was athletic and he nailed his audition - choosing to enact the moment when Robinson is at his angriest and most volatile.
It occurs when Robinson has been pushed to the breaking point by the taunts of a racist manager (Alan Tudyk), and retreats to the dugout to explode out of view of the public.
"I felt like that was the scene that spoke to the way I would play the role," said Boseman, who'd been tossed the script the night before.
"I thought if I played the less explosive scene, I'd be playing passive, and I'm not going to be doing anything," he said.
Later, when researching the role, he learned that there was so much going on in the "passive" Robinson.
"I think that some people may have this notion about Jackie, that he was passive, but that's not who he was as a person," said Boseman, who cited Robinson's activism in the military, a stance that led to a court martial.
"He was a fighter, there was a fire under him, that's what I wanted to convey, and that's one of the things that I hope comes through," he said.
Boseman's road to "42" starts with his road to acting, which truly started all the way back in South Carolina, where he grew up in a middle-class family, and was drawn to the arts. His brother took up dancing, while Boseman started writing, performing his own plays, and enrolled in Howard University with an eye to becoming a director.
That led him to Oxford University, then to a career writing theater in New York and Chicago, and to acting jobs. His chance at playing Robinson is one of those weird Hollywood stores of fate and chance - he'd been auditioning for a role in "Django Unchained," didn't get the part, but caught the eye of the casting director, who recommended him to Helgeland.
He got the role, then had a second and perhaps more important audition - with Robinson's widow, Rachel (played in the movie by Nicole Beharie).
She gave him valuable insight.
"We talked about his incredible discipline," Boseman said. "How he was adamant about not doing anything in public that might cause people to fault him unnecessarily. But she made a point of insisting that I also show what a warm person he could be, and playful."
Still another audition: Boseman, a playground basketballer as a kid, had to learn to play baseball, and to look as though he could play it as well as Robinson.
"Baseball is daunting, there's an unbelievable skill set there," he said. "You can be a good athlete, but being able to throw the ball from deep short to first is a special skill. Hitting a ball to a particular spot, even hitting it at all."
He endured grueling baseball boot camp, and spent hours imitating Robinson's on-field mannerisms, his batting style. They'd shoot it, and watch it on a split screen next to archival footage of Robinson.
Very labor intensive but, in a way, it was the easy part.
"Your challenge is to make him a fully realized man," Boseman said. "Jackie doesn't always know how big what he's doing is. He's not thinking of himself as a future icon. He's just trying to do the right thing in the moment. Hopefully, and I think this is what the movie is about, that's what we're all doing."