Rize (PG)

In fact, Rize offers a genuinely fascinated, no-frills account of its subject - a manic, electrified dance style, sometimes performed by young men and women got up as clowns, with faces painted in a delicately fancy fashion that's more Venice Carnival than Ronald McDonald.

The phenomenon began with Tommy Johnson, a genial, round-faced man whose destiny was made the day that - so the myth goes - he was drafted in to perform as a clown at a children's party. Tommy the Clown became an influence on local children and teenagers, impressing them with buffoonery, wild footwork and tough love. He runs a Hip-Hop Clown Academy, and the phenomenon has spread, with some 50 clown groups now in existence around LA. They have apparently made a big social difference; one mother says, kids now have a choice between the gang life or clowning. Whether that's true or not, you can see the appeal of Tommy's softer, sillier hip-hop option, with its bring-the-family inclusiveness: LaChapelle even films a toddler in a romper suit doing the moves.

With his rainbow-coloured afro and crew of supporting dancers, Tommy is clearly better value at a kids' party than any number of balloon benders. But not everyone favours his happy-clappy approach. The breakaway alternative to his style is the more brutally adult "krumping". Judging by the crowds of bare-chested boys hurling themselves into a frenzy, krumping seems to owe something to the mosh tradition of the LA punk scene, and brief ritualised spats suggest a touch of capoeira. Some girls demonstrate the "stripper dance", which involves arse-wobbling in a dancehall style that seems more jokey than Jamaican.

Nothing if not eclectic, krumping/clowning is dynamically watchable. A caption assures us that the footage hasn't been speeded up: in fact, the dancers look more as if they have been animated by stop-motion, as they twitch and jerk through galvanic flurries of movement. There are only distant echoes of old-school breakdancing: this is crazier, more cartoonish. One dancer's signature trick is to grasp her ankle between her teeth.

Quite how seriously Rize takes its subject is shown by the opening documentary inserts of the 1965 Watts riots and the Rodney King riots in 1992. Today, the film argues, krumping provides a vital outlet for social tensions, and LaChapelle's subjects line up to tell how dancing - and not infrequently, churchgoing - saved them from drugs, prison or worse. When they talk about how dangerous South Central is, they're not kidding: late in the film, we hear about the sudden, apparently random shooting of a 15-year-old girl, Quinesha Dunford, to whom Rize is dedicated.

In a grimly comic sequence, which could almost be a vintage Richard Pryor routine, a chuckling elderly man, presiding over a coffin shop, tells a visiting youth, "Lot of people think us old folks are doin' all the dyin', but you young folks are beatin' us outa here, boy." Even within the dance scene all is not sweetness and light. At a clowns-vs-krumpers contest, there's bad blood when the clowns win, and Tommy returns to find his house ransacked (in this film, you really do see a clown cry).

Rize is more vivid than insightful. LaChapelle is excited by the scene, but doesn't seem to have an angle on it, other than to celebrate its dynamism and, at one excruciating point, to compare it to African tribal dance by cutting in black-and-white archive footage. Overall, this is surprisingly sober film-making: LaChapelle is clearly determined to play down his reputation as a flamboyant artificer. There is a handful of images, however - dancers framed against an intensely blue sky, kids posing on a pink bedroom wall - that jump out at you as pure David LaChapelle.

For the most part, though, Rize is an enjoyable, enthusiastic, slightly by-the-book example of the currently popular American mode of inspirational documentaries about individuals pursuing a dream against the odds (Murderball, Spellbound - and I suppose we'd have to include that penguins film too). Rize doesn't quite convince us that krumping and clowning are more socially significant than any other current black-culture phenomenon. But it comes as a pleasant surprise to see any American film in which "clown" doesn't automatically signify "serial killer". And any dance movement for grown-ups that involves bouncy castles has got to be a good thing.

j.romney@independent.co.uk