It’s only right that so many characters in Uncle Drew don throwback jerseys. The entire endeavor celebrates the old school — from its conceit of senior citizens schooling young’uns to the congenial, casual and chummy ’90s sports comedy vibe it so effortlessly conjures.

Uncle Drew is adapted from a series of Pepsi Max promotions in which NBA superstar Kyrie Irving — a Cleveland Cavalier when the spots began, now a Boston Celtic — wore old-man makeup and showed up youthful street-ballers as the title character. He and LeBron James won an NBA Championship together, but there’s almost certainly no Sprite movie in LeBron’s future. Or at least let’s hope not.

Written by Jay Longino and directed by Charles Stone III (who, between Mr. 3000 and Drumline, knows this genre well), the feature-length version is similarly low-calorie and sugar-free. Tinny and saccharine at times, but ultimately crisp, sharp and caffeinated by a cast consisting chiefly of former NBA and WNBA superstars.

A 30 for 30 spoof prologue establishes the premise: If Harlem’s Rucker Park was a mecca for streetball, Uncle Drew was the reason people made a pilgrimage. Throwing down with one hand while his other held a ham sandwich, Drew and crew were unstoppable. That is, until the team mysteriously ghosted on the Rucker Classic finals and were never heard from again. A parade of famous faces, and a passel of good spoof jokes, set the tone right.

Decades later, sneaker salesman Dax (the irrepressibly likable Lil Rel Howery of Get Out and NBC’s The Carmichael Show) has mortgaged his life savings putting together his own team to manage and win the 50^th Rucker Classic. In basketball, the orphaned Dax found a diversion from drudgery. It also gave him heartache, after a mishap costs his team a championship and causes a lifetime of on-court jitters.

It’s bad enough that Mookie (Nick Kroll) blocked Dax’s shot. Now he’s stealing Dax’s star player for his own Rucker team and Dax’s girlfriend (the ubiquitous Tiffany Haddish, demonstrating that her weaponry is only as effective as a director knowing where to aim it, as Stone does not). Destitute, homeless and without a team, Dax stumbles upon Uncle Drew shaming a younger, flashier player with some electric boogaloo and half-court treys. (“Time for you to change your PIN number ’cuz you just got robbed,” Drew taunts, the hobbling making it even funnier.)

Here, Irving’s clear vision for what the character could represent beyond a soda shill gives Uncle Drew unexpected heft. If Dax haunted by his hang-ups, Drew is haunted by his hype. Once the toast of the game, he’s now just an itinerant irritant to East Coast “youngbloods” living out of his tricked-out shaggin’ wagon. Drew let his ego run the clock out all those years ago. In accepting Dax’s pitch to round up a team, Drew sets out trying to amend all that he did wrong.

So begins a Blues Brothers style road-trip to assemble the gang and boy, does Stone know how to work with them. Ship to stern, this is the best cast of non-acting athletes in a sports movie.

There’s Chris Webber — nearly unrecognizable under his elderly latex, channeling Arsenio Hall’s Reverend Brown from Coming to America and funny as hell — playing the exuberant Preacher, with Lisa Leslie as his skeptical wife, Betty Lou. (Yes, there’s a terrific timeout joke. Yes, Leslie gets to ball as well.)

As the seemingly blind Lights, Reggie Miller gets some goofy, gracious laughs … and, eventually, the chance to resurrect that deadly jumper with which he once gave Bulls fans like this one the vapors. Three-time slam-dunk champion Nate Robinson plays Boots, a mute retiree in a wheelchair whose reflexes and resolve reawaken once Drew turns up.

Finally, there’s Shaquille O’Neal as Big Fella, indomitable in the paint and disdain for Drew. Talk about staring down past regrets: It’s the entire M.O. for Shaq’s presence here. He’s introduced running a dojo (with immediate memories of the Shaq Fu fiasco) and, well, let’s just say Shaq’s performance at the charity stripe outdid anything he ever did on a screen since Blue Chips … at least until now.

Initially invalid as a collective squad, Drew, Preacher, Lights, Boots and Big Fella eventually shake off the dust to shake things up at Rucker Park. Only intermittently can you sense Longino straining to stretch the film out — particularly in a third-act medical emergency that nevertheless gives Shaq room to stretch his giant self for a low-key great bit of physical comedy.

There are dance-offs, confrontations, resolutions. And if you don’t think Dax will get back out there in another championship, well, enjoy your first sports comedy. At least, for a subgenre in short supply these days, Uncle Drew is a good one with a relaxed, retro charm all its own.