Rocky takes on Jake LaMotta more than forty years on in “Grudge Match,” and though I won’t spoil the ending by telling you which of them wins, the audience certainly loses. The latest example of a nostalgia-soaked Hollywood geriatric comedy is undercut by a script that, even by the low standards of the genre, is poor. But it’s totally undone by a last act so unpleasant that its target viewers will probably be turned off by the excessive carnage.

The script by Tim Kelleher and Rodney Rothman lays out the backstory quickly. Once upon a time Henry “Razor” Sharp (Stallone) and Billy “The Kid” McDonnen had traded championship bouts, with McDonnen taking the first fight and Sharp the second—and the belt. A rematch was scheduled, but before it could happen Sharp abruptly retired without explanation, leaving Billy fuming.

Now Dante Slate, Jr. (Kevin Hart), the motormouth son of their old promoter, approaches each of the men with a proposal to work with a video game manufacturer to don motion-capture suits for data that will allow players to engage the duo “virtually” in their long-delayed fight. McDonnen, an aging playboy who owns a bar and car dealership, agrees at once, but Sharp, who’s settled into a simple life working at a Pittsburgh foundry, demurs until a layoff leaves him without the cash to pay for the nursing-home treatment of his erstwhile trainer Louis “Lightning” Conlon (Alan Arkin). Predictably, the studio session turns into a brawl between the two that’s captured on a cameraphone and goes viral on YouTube, leading Slate to propose a real return match to be known as “Grudgement Day.”

What follows on the boxing side is awfully predictable. The two men are coaxed into a series of embarrassing marketing ploys, in one of which Sharp decks a much younger martial-arts star. The two guys train, Sharp under the tutelage of tart-tongued Conlon and McDonnen in the gym of ex-champ Frankie Brite (LL Cool J), but under the bored gaze of overweight has-been Mikey (Joey Coco Diaz). It goes without saying that these scenes are meant to be goofy reminiscences of the stars’ earlier movies.

But the script naturally has to make room for sentimental subplots too. So who should suddenly show up but Razor’s old girlfriend Sally (Kim Basinger), a recent widow who pleads with him not to fight. Meanwhile her son B.J. (Jon Bernthal), a coach, introduces himself to McDonnen as his—a fact that pretty much explains the reason behind Sharp’s original decision not to give Billy the rematch he wanted so badly. B.J. soon not only takes over as Billy’s trainer but introduces the old man to his cute-as-a-button grandson Trey (Camden Gray). (Oddly, there’s never any mention of what happened to the boy’s mother. Or an explanation for why they’re living with Sally.)

In what follows, the only really amusing moments come from Arkin, who’s doing his familiar ornery man shtick. But it’s good shtick, and director Peter Segal knows it, training the camera on Arkin as often as he can and encouraging him to play to the rafters as he delivers his abrasive lines, forces Stallone to soak his hands in horse urine to toughen them up, or does a derisive jig when Razor finally takes Sally’s calls. The more “dramatic” stuff centered on Razor (especially a physical problem that comes out of left field and serves as a major plot point at the end) is a complete washout, but there’s some modest interest in the fact that McDonnen is portrayed as pretty much a louse—even when he tries to bond with Trey—and De Niro actually plays him that way. The characterization undermines the essentially good-natured feel of the picture, but at least there’s some bite to it. Or to put it another way: De Niro might have become the Olivier of his day (remember “the Betsy”?), taking roles in dumb movies for a paycheck, but at least he brings a bit of the old ferocity to them.

Unfortunately, the final match-up does go on, and a nasty business it is, with the stars flailing away at one another for a full fifteen rounds, though it frankly feels like fifty. They wind up bloodied and exhausted, but viewers will feel battered too, even if the script finds a way to endow the codgers with a touch of old-time sportsmanship to make the unsavory business seem less grotesque.

Apart from De Niro and Arkin, nobody in the cast appears to be much interested except for Hart, whose turn as a fast-talking hustler is a lot less amusing than it should be, except for when he exchanges barbs with Arkin or appears in the final credits trying to arrange other “reunion” fights with the likes of Mike Tyson. Basinger is totally wasted, Bernthal is bland, and LL Cool J demonstrates once more that celebrities need to take some acting lessons before they step in front of a camera. If you watch closely you can spy Anthony Anderson in a one-scene cameo as a nursing room orderly; why he took such a throwaway part is a mystery. Technically the movie is just okay, though you have to credit Segal, cameraman Dean Semler and editor William Kerr, as well as the actors, with keeping the final fisticuffs from appearing totally absurd, even if they’re hardly a model of plausibility.

“Grudge Match” doesn’t wind up face down on the mat, but this recycling of “Grumpy Old Men” with boxing gloves certainly loses on points.