The nerd patrol

Jonah Hill seemed entirely serious and a bit panicked as a rather unusual lawbreaker advanced toward him, ignoring profanity-laden orders to halt. With a prop gun wavering in his hand, Hill implored the perpetrator to think of his family and warned that he wouldn’t hesitate to shoot.

But the little white duck waddling through Lafreniere Park barely acknowledged the human in a bicycle cop’s summer uniform of navy blue shirt-sleeves and shorts. It just continued to make its way toward the pond in the center of the park as the “21 Jump Street” crew stifled its laughter until the film’s directors, Phil Lord and Christopher Miller, could call an end to the silliness.

“The secret with Jonah is just having a long enough magazine of film -- and not cutting,” Lord said .

That sequence on a balmy day last May was just one of the heavily improvised moments captured for the movie, which opens in theaters Friday. Like its source of inspiration -- the late 1980s cult TV series “21 Jump Street” that launched Johnny Depp’s career -- the Sony Pictures film centers on young-looking police officers posing as high school students to solve crimes. Instead of a multiracial cast tackling important issues, though, this is a raunchy bromance featuring a mismatched pair of bumbling cops (Hill and Channing Tatum) who go undercover to bring down a drug ring.

Their mission puts them at odds both with the students atop the school’s social ladder, including the ecologically minded Eric (Dave Franco, James Franco’s younger brother) and a gang of thugs run by the heavily tattooed Domingo (DeRay Davis). But what really trips them up is the way teenage life has changed since the days when Tatum’s brawny Jenko bullied Hill’s brainy Schmidt.

“To me the big hook of the movie is that when they get there, high school has changed so much,” Lord, 36, said. “We’re in this weird heyday of the nerd. ... Now it’s cool to wear skinny jeans, and Devo is a cool band. You’re not a loser for liking comic books or playing video games. It used to be that’s what losers did. It’s like Jonah finally found his time. History finally caught up with Jonah Hill.”

Hill’s agent pitched the concept to the actor about five years ago, and after some initial reticence he sparked to the idea and brought it to the studio and producer Neil Moritz. It was just as Hill was making a name for himself with the 2007 films “Knocked Up” and “Superbad.” Hill’s busy schedule kept the project at bay, but after he finished what would become his Oscar-nominated turn in “Moneyball,” “Jump Street” took shape with a script from Michael Ball (“Project X,” “Scott Pilgrim vs. the World”).

The film marks the live-action debut for Lord and Miller, who met as freshmen at Dartmouth. Although their sole previous feature was the animated family movie “Cloudy With a Chance of Meatballs,” the pair -- who watched “21 Jump Street” as teens -- were eager to direct the R-rated film not only to demonstrate their range but also because they were excited to bring back the buddy action comedy.

“Some of those movies are just arguing -- there’s plenty of arguing -- but you want to root for their relationship and want them to stay friends when they have that inevitable breakup,” said Lord, who cited “48 Hrs.” and “Running Scared” as reference points. “You’re rooting for these guys to figure it out.”

On set, Hill, 28, and Tatum, 31, appeared to have no problem figuring out their rapport, casually improvising and laughing as they shot some scenes for the movie’s opening: Before Schmidt and Jenko are assigned to the Jump Street program, they’re on bike cop duty, which isn’t as glamorous as the characters imagined police work would be.

They killed time sitting on a picnic table and retrieved a Frisbee from the lake for some extras before Hill tried to take down that duck solo.

“When the cameras stop rolling they will prank each other and try to make each other laugh,” said Miller, 36. “They have a very playful chemistry just naturally. We’re trying to do whatever we can to harness what they actually already have.”

Tatum, who has mostly appeared in action movies and some dramatic fare, called the experience an “eye-opener.” “I’ve never done so many table reads, just reading the script out loud to see what’s funny, what gets laughs, what doesn’t get laughs, and having all your friends come in and listen to it be read,” he said. “It’s such a different way to make a film. I love it.”

The box office prospects for the roughly $40-million production likely have been served by Tatum’s success in the recent romantic drama “The Vow” and by efforts to play up the film’s hipster credibility. “21 Jump Street” premiered Monday at Austin’s South by Southwest Film Festival -- the same place “Bridesmaids” debuted last year -- and Hill and Tatum will head to Anaheim on Friday to promote the movie at WonderCon, a sister event to San Diego’s Comic-Con International.

Well before those plans were in place, though, Hill (who, along with Tatum, is an executive producer on the film) predicted that the movie would find its audience.

“The best thing we have going for our movie is that people assume because it’s a remake of a TV show that it’s going to be bad,” said Hill, still sporting his bicycle cop attire. “For me, the people that love the show who are older and were around when it was on will go see it if they have nostalgia for it or they think the trailer looks awesome. The young people will go see a movie if they think it looks cool.”

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gina.mcintyre@latimes.com