Nicolas Cage, left, plays the title character in “Joe,” the boss and surrogate father of a troubled teen (Tye Sheridan, right). (Lionsgate Films)

Nicolas Cage is the biggest name in “Joe.” That doesn’t mean he’s the star.

Though the film, out Friday, is a powerful reminder that Cage can, in fact, act (regardless of what the “Ghost Rider” movies suggest), some of its best performances come from the supporting cast — many of whom had never acted a day in their lives. They were just waiting in line at a day laborer center in Austin, Texas, when director David Gordon Green (“Pineapple Express”) showed up.

“You go down at five in the morning and there’s a line around the block of people looking for work,” Green says. “A construction foreman will go by and say, ‘I need a guy who can do drywall,’ or another guy will go, ‘I need one guy that’s good with a chainsaw up in a tree.’ I was scouting for their faces. They wouldn’t know when they were lining up at 5 a.m. they’d spend the day acting with Nic Cage.”

In the film, most of the men portray workers hired by a construction company to poison and kill trees standing in the way of development. Joe (Cage) is their foreman, and when Gary (Tye Sheridan), a hardworking teen with a troubled family life, shows up for a job, Joe takes him on — first as an employee and eventually as a surrogate son.

Gary desperately needs a father figure, as his own dad, Wade, is a drifting alcoholic with a violent streak that hovers dangerously close to the surface. In what may be the most impressive debut performance in film history, Gary Poulter dominates as Wade, imbuing every scene he’s in (and even some he’s not) with a menacing, mesmerizing presence. Oh, and he wasn’t a trained actor, either — he was a homeless alcoholic living on the streets of Austin.

“He didn’t go to Juilliard, but he trained in his own way,” Green says. “He had a lot of his own life and depth to bring to the table.” Poulter died two months after filming concluded, drowning in 3 feet of water while intoxicated near a lake in Austin.

Green dedicated the movie to him and says “Joe” could never have packed its emotional punch without the corps of untrained actors.

“People that have a lot of charisma don’t need a lot of training,” Green says. “A lot of actors are busy fixing their hair before their close-up. These guys were always ready to go to work.”