A rowdy Irish rap trio with a growing sense of purpose tells its own story in ‘Kneecap’

A pair of proudly Irish-speaking lads stump for their marginalized native language when they become underground rappers in the box-bursting, enjoyable “Kneecap.” That’s also the name of the real-life West Belfast outfit whose origin story — juiced for maximum political energy and comedic verve by writer-director Rich Peppiatt — makes for a tub-thumping, fist-pumping good time.

Sure, Naoise Ó Caireallain, Liam Óg Ó Hannaidh, and JJ Ó Dochartaigh — known respectively under their rap monikers Móglaí Bap, Mo Chara and DJ Próvaí — could have gone the traditional documentary route, charting their rise from defiant West Belfasters to internationally recognized cultural heroes. But where’s the fun in one more interviews-and-clips movie when you can instead play yourselvies and forge your own remix of “A Hard Day’s Night” or “The Harder They Come,” flecked with a little bit of “The Commitments” to boot?

Growing up “cease-fire babies” in the wake of the Good Friday Agreement but still feeling the youthful despair of oppressive Unionist rule, childhood besties Naoise (Ó Caireallain) and Liam Óg (Ó Hannaidh) take to heart what Naoise’s dad, Arlo (Michael Fassbender), a car-bombing legend in the IRA, used to instill in them: “Every word of Irish spoken is a bullet for Irish freedom.”

Arlo, though, is absent and presumed dead, and Naoise’s mom (Simone Kirby) has become a shut-in. And while the movement to legitimize the Irish language in Northern Ireland gathers steam, Naoise and Liam Óg are little more than clubgoing miscreants just trying to get drugs to either take or sell.

When Liam Óg gets arrested and refuses to speak English to his interrogating officer, mild-mannered music teacher JJ (Ó Dochartaigh) reluctantly steps in to translate. What he finds in the detainee’s rambling journal of his sex-drugs-kick-the-Brits-out lifestyle is the kind of rough poetry that’s only a beat track away from being a rebellious new form of hip-hop.

With the two friends drawn to the notion, and JJ agreeing to hide in plain sight as their tricolor-balaclava-wearing DJ (there’s wonderful irony in a militant mask helping this guy keep his respectable day job), the newly formed trio goes from impudent pub-stage oddity to community firestorm. As Kneecap’s outspoken music and ketamine-fueled antics give their listeners a pulsating new reason to learn (and protect) their home language, the group also finds itself a fresh target for authorities — including the Republicans’ own self-policing paramilitaries — who find their influence worrisome.

Music-filled and spikily edited, “Kneecap” finds rude wit and edge to underscore its needle-drop righteousness; that it sustains its level so exuberantly is remarkable, especially considering how hit-and-miss these self-mythologizing projects often are. The performances are a punchy combination of skilled and personality-driven, with the appealing Ó Dochartaigh the likeliest candidate of the main trio to land more acting gigs. In all, director Peppiatt (who is, funnily enough, British) is a savvy ringmaster of the story strands, acting styles, tones and his stylistic flourishes, which call to mind the freewheeling zest of “Trainspotting”-era Danny Boyle.

It’s rousing and never tiresome. Peppiatt not only makes drug humor seem joyfully silly again, but treats Irish patriotism as a tempting high worth celebrating; there’s a tough and satiric love at play. Inside the beating rebel heart of “Kneecap” is a bruising comedy of manners — it’s as emotionally attuned to the divides between people on the same side as it is gloriously cheeky about the kinky attraction Liam Óg has for British squeeze Georgia (Jessica Reynolds).

Every Irish speaker in “Kneecap” wants to be seen, felt and heard in their fight for freedom. That funny, funky riot of attention-seeking pain and pleasure, inspired by the pioneering voices of American hip-hop, makes for a bracing, entertaining transatlantic dispatch.