Inspired by real life, "American Underdog" tells the story of how Kurt Warner went from bagging groceries in a supermarket to becoming a Super Bowl-winning quarterback and NFL Hall of Famer. Starring Zachary Levi, Anna Paquin, and Dennis Quaid. In theaters Christmas Day.

Even as his story first was unfolding in 1999, Kurt Warner heard the buzz: "This should be a movie!"

Now it is.

"American Underdog," the story of the undrafted Hall of Fame quarterback by way of stocking shelves at an Iowa supermarket, is coming to theaters on Christmas Day.

For Warner, it is the satisfying conclusion to a moviemaking journey that began in earnest when he retired after the 2009 season but did not come together until more recently.

"It really started about three years ago, when we figured we had the right team," Warner told Newsday. "That is when it really became one of those things that we thought, OK, this could really, really happen."

It really has, in the form of a mostly straightforward sports biopic starring Zachary Levi as Warner, Anna Paquin as his wife, Brenda, and Dennis Quaid as Rams coach Dick Vermeil.

Warner has experienced the emotions most living subjects of scripted films do, especially the fact that it was "definitely strange, definitely weird" to see another person pretending to be him.

The trick not only is getting used to someone else being you — it helps that there is a strong physical resemblance between Levi and Warner — but also that filmmaking is not meant to be an exact reenactment of events.

"You go into this and think it’s supposed to be a documentary and it’s supposed to be laid out word for word and action for action based on the way it happened," he said. "At the end of the day, you understand it’s a movie.

"Although it’s based off real-life events — and those stories that are a part of your life — how it plays out on the big screen is a touch different than how it played out and how it felt when you went through it in real life."

Warner said what really mattered was the writers, actors and production team getting "the essence of the story correctly. They don’t have to have every mannerism. They don’t have to say it in exactly the same words.

"Once you get comfortable with that, that’s when you can really step back and get excited about the message that is told."

Warner believes the film delivers in that regard, including acknowledging the importance of religious faith in his and his family’s lives.

But even though the film was directed by brothers Jon and Andrew Erwin, who specialize in films with Christian themes, that element of Warner’s story is told without dwelling on it. That was intentional, he said.

"That was always going to be an element of the movie, because that’s who we are and that underlies everything about us," he said. "But at the same time, we wanted to make a movie for everybody — a movie that can meet everybody where they’re at and challenge them in different ways."

He added, "We’re not here to tell everybody where they should be or what their journey should be. Our goal was to share our story how it played out, and faith was obviously a part of that — and a big part of that."

Warner, 50, played in three Super Bowls with the Rams and Cardinals and won one.

But he credits his 2004 Giants interlude between his St. Louis and Arizona years as pivotal, even if he did start only nine games — totaling six TD passes and four interceptions — while keeping the position warm for rookie Eli Manning.

Warner was 33 at the time and looking to prove he still had some good football in him.

Warner initially was frustrated that the Giants were focused on running the ball on offense, a stark change from his "Greatest Show on Turf" days with the Rams.

Looking back, though, he sees that as a positive. "[I realized], hey, this is what being a quarterback, this is what being a leader, is all about," he said, "being able to learn how to lead and to be successful in different ways."

The Giants were 5-4 when first-year coach Tom Coughlin benched him in favor of Manning, who went 1-6.

"I was able to do enough in those nine games to convince a few teams, specifically the Arizona Cardinals, I could play," he said. "Obviously, it worked out well in the long run. I was able to get back to where I wanted to go."

Now he is watching it unfold all over again, on the big screen. The parts about his personal life might have been a little uncomfortable, but historically it is more difficult for filmmakers to get the sports part right.

"I can’t sit here and expect Zachary Levi to look like me — who’s been throwing a football for 40 years of my life — in four months to be able to do that," Warner said. "Or you get these doubles and even guys who have played football at different levels, and to expect them to play Marshall Faulk and Isaac Bruce [is unrealistic]."

That said, Warner believes the filmmakers did a "great job" with the football scenes, including recreating plays that actually were used by the ’99 Rams.

"No sports movie is going to look exactly like the real thing," he said. "But I believe our people pulled it off really, really well so that people are going to be very engaged in the football scenes."

Twenty-two years ago, it was a story made for Hollywood. Now, at last, it is a story made by Hollywood.

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