Grade: B+

It’s usually bad news for a picture to open not long after a movie with a similar theme, but in the case of Karyn Kusama’s debut feature the rule doesn’t apply. “Girlfight,” a Sundance favorite about a troubled teen who finds fulfillment as a boxer, appears only a few short months after Lorenzo Doumani’s gender-reversal “Rocky” ripoff “Knockout,” and comparisons are universally in favor of the newer flick. “Knockout” was trite, clumsy and hamfisted; Kusama’s film is natural, unforced and surprisingly compelling.

The plot is, quite frankly, just a distaff version of numerous earlier pugilistic exercises (think of the recent British “TwentyFourSeven” or even the documentary “Southpaw”) in which a young person headed in a downward spiral learns self-respect and discipline (and sometimes romance) in the ring; but as it’s written, directed and played it avoids almost all the banality and mustiness of the genre. It centers on Diana (Michelle Rodriguez), a Brooklyn highschooler whose campus career is none too stellar and whose home life is at best difficult. Her father Sandro (Paul Calderon) foots the bill for boxing lessons at a local gym for her decidedly unathletic brother Tiny (Ray Santiago), an aspiring artist, but before long it’s Diana whose using the cash to train under Hector (Jaime Tirelli), a coach who gradually develops a paternalistic interest in her success. The heroine also builds a relationship with another boxing student, Adrian (Santiago Douglas), which causes more than a bit of trouble when they’re scheduled to fight one another.

In less skilled hands, this storyline could have been deadly: one can imagine the characterizations being overblown, the cliches exaggerated, and the finale turned into a rah-rah sort of “Rocky” bout–certainly “Knockout” fell into all these traps. But here the tone is much more naturalistic and restrained, and the characters have been given dramatic heft and resonance. Rodriguez is astonishingly good as Diana, turning her into a figure who gains audience sympathy while remaining realistically sullen and unsure of herself and never becoming mawkish, and Tirelli–who resembles a thinner, scragglier version of Joe Mantegna–gives a nuanced reading of her coach, neatly skirting all the mannerisms one might anticipate. Douglas matches Rodriguez as the young man who comes to respect and love her; he nicely underplays the fellow’s cockiness, giving Adrian a touching sense of insecurity too. Even the less admirable characters are drawn with surprising shading: Sandro, for instance, is not a likable figure at all, but as Calderon plays him, Diana’s father has an aura of regret as well as anger about him.

The success isn’t simply due to good acting, of course: it’s fundamentally Kusama’s knowing, intelligent script and her equally subtle direction that drive the picture. One notes that John Sayles and his partner Maggie Renzi, who have collaborated on so many excellent independent films, had a hand in assisting with “Girlfight,” and perhaps their expertise has rubbed off (Sayles also does a cameo as one of Diana’s teachers). But mentioning that in no way diminishes Kusama’s accomplishment. Apart from some problems with the lighting, which gives many sequences an uncommonly dim look (this may be the fault of Patrick Cady’s cinematography: the settings should be dingy and dark, to be sure, but we should nevertheless be able to see what’s going on in them), hers is a remarkably assured and impressive debut. “Girlfight” is a small film, and you might have to search for it, but it’s well worth the effort.