They say there's an exception to every rule. When the generalization is that pro wrestlers should not be actors, I propose a loophole for Dwayne "The Rock" Johnson.

Although he started out in movies that exploited his prowess at grabbing his fellow actors and smashing them, he has evolved into a solid performer. He's got terrific screen presence, he's got the range to play heroes, villains and clowns, and he brings a certain core honesty to his characters. In "Gridiron Gang," he takes on a role we've seen hundreds of times before — a football coach whipping a ragtag team of misfits into a proud, disciplined unit — and makes it true and fresh. His latest film is a first-class showcase for his talents.

Johnson plays Sean Porter, an L.A. corrections officer at a facility for juvenile felons. The unit's mission is simple: Keep them off the streets and keep them from killing each other. Porter launches a football program to pull them out of a macho culture of violence. He uses the game to teach them discipline, pride and teamwork.

The film is energetic and technically polished, with flashes of humor ("I thought we had an agreement: No killers on the football team!" blusters a warden) and slashes of gang violence. Its main distinction, though, is its ambivalence about the shooters, stabbers and thieves that make up Porter's team.

Director Phil Joanou, veteran of many U2 videos, shows us the foul ecosystem they came from, a place where teen boys on low-slung bikes keep pistols in their waistbands. The introductory narration implies the juvie jailbirds are just kids who made a huge, life-shattering mistake, but the film frequently reminds us of the hard truth of the situation: This gangbanger stabbed an old woman for her purse and that one shot his stepdad.

Porter sees something salvageable in many of them and pushes them until they recognize it in themselves. The premise is nothing novel or fancy, but it works. Their metamorphosis from stumblebums to gutsy contenders for the championship is slow and frustrating, but the push-push-pushing Porter is a powerful mentor.

Johnson makes him inspirational without going sappy. His standout scene comes when the junior convicts make a surprising gesture to honor his dying mom, and coach, touched to his core, struggles to keep his composure. Though it sounds saccharine, Johnson plays it straight. Because the filmmakers avoid unfair manipulation, the moment puts a lump in the throat.

The ending is warm, but not the conventional stand-and-cheer rouser. "Gridiron Gang" is wise enough to show us that even partial victories are worth the struggle and hope can be its own reward.

<b>TITLE:</b> "Gridiron Gang"<b>DIRECTOR:</b> Phil Joanou<b>CAST:</b> Dwayne "The Rock" Johnson, Xzibit, L.Scott Caldwell<b>RATED:</b> PG-13 (some startling scenes of violence mature thematic material and language)<b>GRADE:</b> 3 Stars (out of 5)