“Blackjack: The Jackie Ryan Story” is a slow motion train wreck about a slow-motion train wreck of a basketballer.

That doesn’t mean that this story of a Brooklyn playground “legend” who never got out of his own way when it came to realizing his hoops potential isn’t interesting, here and there. There’s a decent performance or two, and a time-honored “redemption via sport” formula that has, on occasion, worked.

But as our lurching lead lumbers through middling on-court action, as we grimace at veteran heavy Robert Davi’s version of an Irish American priest, with every “Never saw THAT coming” blast of melodrama, “Blackjack” rolls craps.

Greg Finley, a character actor since childhood (“The Secret Life of an American Teenager”), seems awfully earthbound to be a basketball prodigy approaching his late 20s expiration date. He’s a burly presence on the court, and when guys like sportswriter Peter Vescey (Geoffrey Cantor) describe the “most perfect jump shot you ever saw,” we aren’t fooled. We’re practically looking at a middle school set shot.

“White men can’t jump” indeed.

Jackie grew up in a big, racist New York Irish family, headed by Big Jack (David Arquette), a short tempered construction worker who disdains any sport that isn’t football. Basketball? “Monkeyball” he calls it. His son is destined to “grind it out just like the rest of us.”

We don’t see the kid’s high school hoops skills that New York media hyped into a “white Michael Jordan” label, and eventually eulogized as “one of the biggest wastes of talent in the history of basketball.” Antonio Macia’s script narrows its focus to what amounts to Jackie’s last best shot, the weeks before and after a tryout — at 28 with the (then) New Jersey Nets.

Jackie drinks too much, smokes too much, cusses too much, has too many tattoos and horses around with his disreputable pal and co-worker Marty (James Madio, whose career dates back to “Blossom” and “Hook”). Can Jackie clean up his act long enough to impress Rick Carlisle and the Nets?

The return of old girlfriend Jennie (Ashley Greene of the “Twilight” saga) motivates him. She played in the day, too. Can she get him into NBA shape? She can’t even get him to stop talking about his NBA signing as a done deal.

“Floor seats, FLOOR seats” he promises and/or threatens everybody who hears about his dream. Dude can’t stop smoking and partying, and is so irresponsible he can’t even get a credit card, but OK. Sure.

We know that didn’t happen, so the only mystery here is how close he got and how good he might have been. Actor turned director Danny Abeckaser (“First We Take Brooklyn”) is painted into a corner, a leading man lacking the charisma to make the off-the-court scenes pop, and who plays the game — at 28 — the way Jackie plays it now, like a sharp-shooting fiftysomething.

Sports junkie Michael Rapaport plays a Nets assistant coach (unbilled). But Arquette, Greene and Moise Morancy, playing a neighborhood rival who made it to the NBA give the most interesting performances, with Morancy saying out loud what any basketball savvy viewer must think.

Jackie’s hype and endless “second chances?” They’re ” because you’re white.” Having worked at a newspaper where J.J. Reddick got more ink than everybody else on the Magic put together when he played here, I can totally see that.

That would have been an interesting story thread to follow, as we’re treated to a montage of Ryan’s NYC media hype in the film’s opening credits. What we get instead is a stumbling story about a more obnoxious “Rudy” we don’t like enough to root for, and who never shows us the game that all the fuss is about.

MPAA Rating: unrated, much profanity

Cast: Greg Finley, Ashley Greene, James Madio, Geoffrey Cantor, Moise Morancy, Michael Rapaport, Robert Davi and David Arquette.

Credits: Directed by Danny A. Abeckaser, script by Antonio Macia. A Gravitas Ventures release.

Running time: 1:38