The day Jimmy Smits quit the football team at Brooklyn’s Thomas Jefferson High School to join the drama club shaped his entire life — in his case, a 30-year career as a TV star. But he took a lot of heat from his East New York teammates when he did it. “I was ostracized,” Smits says over lunch at Midtown’s Oceana. “I had to give my [varsity] jacket up. Thomas Jefferson High School had one of the best football teams in the city. My buddies said, ‘You’re going to the theater?’ ”

Smits, now starring in NBC’s “Bluff City Law,” was only 16 when his drama teacher, Mickey Tennenbaum, took him to plays and inspired him to wait on line at Central Park’s Delacorte Theater on weekends to see Raul Julia and James Earl Jones do Shakespeare. “Those two guys specifically gave me permission to aspire,” says Smits, 64. “I just wanted to do what I saw those guys do.”

Under Tennenbaum’s tutelage, Smits performed in school plays, facing a moment of truth during a student production of “Purlie Victorious.”

“I was playing Charley Cotchipee and the football team was sitting in the first two rows of the theater,” he says. “I thought, ‘They’re gonna f–k me up. These guys got tomatoes; they’re going to throw s–t at me.’ ”

Instead, they stood up and applauded him. Smits was on his way, thanks largely to his drama teacher, who was doing graduate work at Brooklyn College. Tennenbaum persuaded Smits to enroll there, where he studied with Bernard Barrow, a working actor and star of “Ryan’s Hope.”

“[Barrow] was able to navigate for me,” Smits says. “He said, ‘You’ve been doing Shakespeare and all this classic stuff. I think you can go to LA and be the crook of the week on “Hill Street Blues.” Or do you want to try out for [something more ambitious]?'”

By then, though, Smits was a father: He and his high school girlfriend, Barbara, had a daughter, Taina, in 1973. Barrow helped him get into the MFA program at Cornell University, where Smits graduated in 1982. “The educational process gave me a tool bag that I could rely on,” he says.

Years of theater and TV work followed before Smits received the script that vaulted him from East New York to Hollywood’s A-list: “L.A. Law.” Steven Bochco and Terry Louise Fisher’s drama starred some of the hottest young actors of the day: Harry Hamlin, Susan Dey, Blair Underwood. Smits played Victor Sifuentes, whom he describes as “idealistic, with a chip on his shoulder … I used to wear sneakers when the camera wasn’t on me because I wanted him to be bouncy.” The role won him an Emmy in 1990.

But Smits, who calls himself “commitment-phobic” when it comes to TV contracts, left “L.A. Law” in 1992, which left him free to replace David Caruso, who vaulted “NYPD Blue” after its critically acclaimed first season. Smits’ Detective Bobby Simone helped the show recover from the gut-punch of Caruso’s abrupt exit and, with Dennis Franz as Detective Andy Sipowicz, carried the police drama through its glory years.

Bochco and David Milch, “NYPD Blue’s” creators, taught Smits the value of self-confidence and collaboration. Even so, after five years, Smits wanted out. And what an exit they gave him: a devastating death scene (from an infection that followed a heart transplant) that was watched by 22 million viewers.

“The contract was up, and I felt the show was kind of very successful,” Smits says. “It was nice that Milch was able to write something that resonated … That’s a remembrance, a little moment that you say, ‘We pulled a couple of heartstrings there.’ ”

‘He was so real that it transcended a TV show.’ - Paris Barclay

Director Paris Barclay calls Smits’ final “NYPD Blue” episodes the high point of his career so far.

“When you have to say goodbye to a consummate professional who embodied a rich and fascinating character, it can be painful,” Barclay tells The Post. “Jimmy made it the saddest joy I’ve ever felt. He was so real that it transcended a TV show — we felt he was actually dying.”

Smits went on to prominent roles as a politician on “The West Wing,” a DA on “Dexter” and, playing against type, the vicious pimp Nero Padilla on “Sons of Anarchy.” Not all his shows were hits. One “clunker,” as he calls it, was CBS’ “Cane,” a 2007 show about a Latino family running a rum business.

“I really felt that there was something special there,” he says. “Then, the writers’ strike happened.”

Smits has high hopes for his new series. Filmed in Memphis — a long ways from Los Angeles, where he’s lived with actress Wanda De Jesus for 30 years — “Bluff City Law” casts him as an idealistic, small-town lawyer who brings his estranged, headstrong daughter (Caitlin McGee) into his practice.

Smits says that filming in the South doesn’t faze him. “It’s one reason that I love doing this thing that I do,” he says. “I get to submerge myself into a different culture, a different area, a different way of talking, a different history.”

Even so, Smits never forgot what it was he gave up to get where he is today. Which is why he treasures the memory of that 1991 day when he was crowned King of Brooklyn in Grand Army Plaza, when his old high school football coach presented him with a custom-made varsity jacket — a copy of the one Smits lost when he left the football team at 16.

“Moe Finkelstein, may God rest his soul, brought my jacket to the King of Brooklyn day,” Smits says. “He got a jacket made for me. I gained a couple of pounds. I still have it. That was the day for me.”