The first shot of the movie "Girlfight" says it all. As people rush to and fro in front of her, Diana Guzman (Michelle Rodriguez) stands still, leaning against a set of school lockers, her head bowed. She looks up and straight into the camera with a glare of pure hostility.

Before we know it, she's picked a fight with an arrogant clotheshorse who is making fun of Diana's plain, plump friend. Brawling seems to be what Diana does best. Her mother died years ago. Her father, Sandro (Paul Calderon), pays her little mind except when he's trying to exert control. Her brother, Tiny (Ray Santiago), wants to be an artist, but Sandro insists that he take boxing lessons. They live in the projects, where hopefulness goes to die.

Diana visits the gym one day on an errand for her father and realizes that this could be a more constructive outlet for her anger. The trainer, Hector (Jaime Tirelli) tries to dissuade her at first but eventually agrees, although Diana must keep it a secret from Sandro.

She learns discipline, self-respect, control. She finds a boyfriend, Adrian (Santiago Douglas), another boxer. And she sets out to take on the true source of her rage.

In other words, except for the gender switch "Girlfight" is in many ways a standard boxing movie. Of course, the gender switch is the whole point. Female boxers have become more prevalent, although they are still a novelty to some. But the movie is less a sports film than a tale of empowerment, and there's nothing wrong with that.

Still, "Girlfight" wouldn't work without the raw passion that Rodriguez brings to the role of Diana in a real breakout performance. Tirelli's tough but warm presence as Hector and Douglas' appropriate bewilderment as Adrian bring out additional facets of Diana's personality.

Even so, the movie strains to find enough variations on its familiar theme to fill its 110-minute running time. "Girlfight" seems to go on too long and some of the plot contrivances, including mixed-gender boxing matches, stretch credulity.

Fortunately, writer-director Karyn Kusama makes up for much of it with her visuals. She gives "Girlfight" a grainy, documentary look in which the primary colors seem to be institutional gray and green. You can almost smell the mustiness of the boxing venues, where ancient men hang around recalling past glories and hoping to observe new ones in the making. She doesn't overplay her hand, either in the ring or in the clinches of the love story.