Whenever there is an uproar over an unarmed black man being killed by police (once a month or so), there is a backlash from people who say the outrage is misplaced. “What about the black-on-black murders that happen every day in Chicago?” they say. “Why isn’t anyone concerned about THAT??” (This is the only time they ever bring it up.)

Well, Spike Lee is concerned about it (evidently), and “Chi-Raq” is his incendiary, satirical take on the subject of gun violence in Chicago’s gang-ridden black neighborhoods. A retelling of the ancient Greek comedy “Lysistrata,” “Chi-Raq” doesn’t offer practical solutions but is instead a venue for Lee and co-writer Kevin Willmott (“CSA: The Confederate States of America”) to vent their anger, frustration, and sorrow in an effort to achieve something else borrowed from Greek theater: catharsis.

The film’s style is appropriately theatrical, with choreographed movement, a musical number, color-coded sets and costumes, and other constant reminders that we are watching a performance. Much of the dialogue (including almost everything spoken by Samuel L. Jackson as the narrator and one-man chorus) is written in rhyme, delivered like a cross between street poetry and Shakespeare, peppered with cultural references both ancient and modern. Whether it works or not (and it mostly does), this creative choice gives the film a rhythmic energy and an even greater sense of theatricality, reinforcing the idea that we’re watching not real life but a fable inspired by it.

The title (pronounced “shy-rack”) is a portmanteau reflecting Chicago’s descent into an Iraq-like war zone. It’s also the stage name of a rapper named Demetrius Dupree (Nick Cannon), a leader of the purple-clad Spartan gang that is forever at war with the orange Trojans. After yet another drive-by shooting leaves yet another innocent bystander dead, Demetrius’ girlfriend, Lysistrata (Teyonah Parris), follows in the footsteps of her ancient namesake and proposes that all women — Spartan, Trojan, and unaffiliated — end the war by withholding sex from their men until peace is achieved. “No peace, no [um, vagina, let’s say]!” is their chant.

It’s a silly plot, not a serious policy suggestion, and Lee lets it play out humorously, getting broad and clownish at times, almost campy. (You’ll enjoy Wesley Snipes as a giggly gang leader named Cyclops, and Dave Chappelle in his brief turn as a nightclub owner whose business is off because of the sex strike.) The story structure probably has other inspirations, but it reminded me most of the “South Park” formula, where a local movement gains worldwide traction in an improbably short amount of time, culminating in a “what have we learned” speech from Stan or Kyle or Lysistrata, all of it meant as commentary on current social conditions.

But while the story is exaggerated and unrealistic, it’s conveyed through authentic characters who speak of real pain. Teyonah Parris’ sexy, fierce Lysistrata is well-matched with Angela Bassett’s Miss Helen, a respected authority figure in the Spartan community who has suffered much loss. Nick Cannon is respectably serious as a gun-loving rapper, and John Cusack shouts himself hoarse as the white priest at a black church who must preside over too many funerals. The rawness of the emotions is palpable, inflamed by Lee’s penchant for provocation and overstatement.

It has plenty of Lee’s loopy indulgences, too, like a bizarre tangent with a Confederacy-obsessed National Guard commander (David Patrick Kelly), and a cameo by Isiah Whitlock Jr. that’s just long enough for him to deliver his catchphrase from “The Wire.” There are jokey references to other Greek plays; some invective aimed at highly specific targets (Darren Wilson; George Zimmerman; the entire state of South Carolina); and an abundance of angry rap, often with the words printed on the screen so we can follow along. In short, it’s a Spike Lee film, and one of his best in a long time — earnest, flawed, idiosyncratic, and unforgettable.

B+ (2 hrs., 7 min.; R, strong sexuality, some nudity, much profanity and vulgarity, pervasive rhyming.)