He's a sexy and sentimental ex-baseball player; she's a dysfunctional and desperate suburban housewife playing mom to four girls. Only "Extra" has your exclusive behind-the-scenes look at Kevin Costner and Joan Allen's new romantic comedy, "The Upside of Anger."

But Joan told us not to expect a typical romance, saying, "It's not a conventional love story at all."

For starters, Joan plays an alcoholic who hooks up with Kevin's character after her husband split. "It's a very personal movie," Kevin revealed. "I've lived in divorce myself, so I recognize a lot that's going on here."

"Life does go on," Joan declared.

"The Upside of Anger," which just premiered at the Sundance Festival, was written and directed by Mike Binder, best known for HBO's "The Mind of the Married Man."

"I wanted to do a fable about what a waste of time anger is," Mike told us. And Mike himself also got some face time in the film, as Costner's co-worker at a radio station.

But there's no arguing about who's at the head of this cast. "Joan is really carrying the movie," Kevin admitted. "She's our lead, and it's really a pleasure to come in and be with her and support her."

And Kevin's convinced he's got a breakout hit on his hands, telling us, "People who love movies, who demand a lot from their movies, this movie is right down the strike zone."

"The Upside of Anger" rages into theaters in March.