The opening credit “A Walter Hill Film” has not graced movie screens in more than 10 years — not since the 2002 prison boxing drama Undisputed flopped at the box office.

That movie’s failure was the last in a series of commercial calamities that plagued the director of popular and cult hits such as The Warriors, The Long Riders and Streets of Fire. Over the ensuing decade, Hill continued to produce movies for other people, but seemed destined never to direct another one himself.

Then Sylvester Stallone called.

“Sly said he had been working with another director on this project who didn’t work out and wanted to know if I’d be interested,” says Hill, 71. “I read the script and said ‘I’m in, as long as you perceive the movie to be an homage to action films of the ’70s and ’80s, and we make it in that spirit — where the engine of the film is certainly not the story, which is preposterous, but the ethical stances of the two lead characters and their opposite world views.”

In other words, Hill wanted to make a buddy-cop movie — not a satire or homage, like Kevin Smith’s Cop Out or Stallone’s own The Expendables, but the genuine article, like 48 Hrs. or Red Heat, two of Hill’s previous hits.

The result, Bullet to the Head, which opens Friday, is based on Alexis Nolent’s graphic novel and centers on the relationship between a jacket-and-tie wearing hit man (Stallone) and a by-the-book Washington police officer (Sung Kang) who team up to bring down a New Orleans crime syndicate.

Stallone is a ruthless, methodical killer (his only rule: no women or children). Kang is a straight-arrow guy with a strict moral code. The two are forced to work together to battle a common foe, creating a gray zone where each man is forced to bend his standards a bit. They’re not bad guys, but their methods are a little questionable.

Hill says he has always been interested in films whose characters must “go beyond the traditional rules and constraints of society to solve the dilemmas they find themselves in.” That’s the prevailing theme of nearly all his movies. In 1981’s Southern Comfort, members of the National Guard must resort to murder to survive a training weekend in the Louisiana bayou. In 1987’s Extreme Prejudice, a Texas ranger resorts to illegal tactics to take down a drug dealer. In The Driver, an obsessed detective seeks the help of a gang of bank robbers to catch a getaway driver-for-hire.

“Stallone’s [hit man] is not a character to be imitated or admired,” Hill says. “But he is a character who is brutally honest about the world he lives in. And the people he is assigned to kill are not exactly exemplars of society. But the critical scene in the movie that breaks ground is when he kills [a villain] who they could have arrested instead. The policeman says ‘You can’t do that.’ And Stallone says ‘At least I shot him quickly and put him out of his misery. Most of the people I know would do it slow to get even.’ That’s the point where the differing philosophies of the two men crash into each other. Who’s right in that situation? You’d have to be Aristotle to figure it out. But Sly definitely does not represent the normal standards of bourgeois society. Is it fair for a movie to give that point of view an articulation?