The pinstriped fans heckle, and the atmosphere grows ever more raucous. As Billy Chapel aims to spin perfection in the Bronx in the final game of the season, a die-hard loudmouth, holding a bag of peanuts, shouts at him from the Yankee Stadium seats: “I’m going to stick a fork in you, Chapel! You’re finished!” The camera spins around the mound, centering on the fictional Tigers pitcher as a subway car rumbles past the right-field bleachers.

“I can always tell when I’m in New York,” Chapel says.

Although For Love of the Game features its main, top-line draw, Kevin Costner, in a Detroit uniform, Sam Raimi’s 1999 baseball drama remains a reverent love letter to the original Yankee Stadium -- its architecture, its energy and most certainly its crowds. In effect, the movie’s backdrop jolts to the foreground, an enduring reminder of how Yankees fans made opposing teams feel each time they visited “The Cathedral of Baseball.”

Which is to say, not great. That aforementioned loudmouth, hurling insults at Costner throughout the movie, was actually assistant director Sean Ferguson, a born-and-bred Yankees fan making a cameo at Raimi’s request. “I’ve been going to Yankees games since I was 5 years old,” he says. “I was just being a Yankees fan and doing what you see in The Stadium.”

Twenty years later, the jeering was one of many contributions crafted to maintain the movie’s steadfast authenticity, arguably its greatest legacy. Never mind the romantic subplot interspersed throughout Chapel’s performance. For Love of the Game shines brightest inside Yankee Stadium, which transformed into a movie set for five weeks and offered plenty of unique challenges to capture a story of baseball immortality.

“It was really special,” executive producer Ron Bozman says. “Going to the Stadium and working out at the field every day, we were the envy of the entire town.”

The movie’s adherence to baseball realism stemmed from the Yankees’ front office. Under guidelines specified by principal owner George Steinbrenner, anyone wearing a uniform needed to be an established actor or real baseball player -- no extras or stunt doubles donning the legendary pinstripes. That suited Costner -- who had played high school ball -- just fine. He brought in friend and legendary college coach Augie Garrido to be a technical advisor, and eventually Raimi cast the University of Texas skipper in the role of Yankees manager. “We used the real batboys, the real ball boys, the real grounds crew, real umpires,” Garrido told Yankees Magazine in 2000. “Steinbrenner played a key role in the selection.”

Garrido, who dressed his own collegiate players in Tigers uniforms, didn’t need to teach Costner any mechanics. Instead, the actor consulted with Yankees pitcher Mike Buddie, who had just finished his rookie season, helping to develop mannerisms and performative elements that seemed authentic. “It wasn’t like we were teaching him what his release point should be,” Buddie says. “It was really like, ‘Tell me if this could be legitimate, something that a Major League pitcher throwing a perfect game would do.’”

Shooting began in late October, shortly after the Yankees had swept the San Diego Padres in the 1998 World Series. As an alternate on the postseason roster, Buddie couldn’t have asked for a better start to his Major League career, spending an extra month inside Yankee Stadium with a few teammates, including Ricky Ledee and Scott Pose. “We upheld the tradition and the brand, which, as a player, I really appreciated,” Buddie says.

Entering the project, Costner was concerned with his knee, which had just been surgically repaired. That quickly changed in the chill of November, when he overused his arm during one of the first scenes the crew filmed. Yankees head athletic trainer Gene Monahan and his assistant at the time, Steve Donohue, came to Costner’s aid with treatment to get him through the rest of the shoot. “He threw 200 pitches, and after that his shoulder was shot; he was in pain,” Donohue remembers. “He fought through it, I can tell you that. It was not a pleasant experience for him throwing those pitches every day.”

“Most of us were totally naive about the wear and tear on a pitcher’s arm,” Bozman says. “It was a learning curve for us, and we figured we had to spread the pitching out in the schedule so we didn’t lose it.” That meant the crew rearranged shooting days, capturing dugout scenes with John C. Reilly, who played the Tigers’ catcher, as Costner rested.

“I tried to explain to the director that this was a man, not a machine,” Garrido said. “He couldn’t warm up and then wait 40 minutes before throwing. He would not have made it without Gene and Steve.”

To enhance the cinematic elements of Costner’s delivery, Ferguson even brought in a few costly lenses, placed the camera behind netting and instructed Buddie to fire fastballs from the mound to capture the ball’s rotation in slow-motion. “He fired the ball at the lens for a half hour, missing it by two inches (nearly) every time,” Ferguson recalls. “He ended up breaking one lens out of the three.”

For all the technical perfection, the biggest challenge was filming inside a stadium that held close to 57,000 seats -- and somehow filling it with people. A couple months before shooting began, Ferguson and a small B-unit crew attended a regular season game to capture fan reactions and wide shots of the entire crowd, occasionally setting up near camera wells to get footage that, when grained down, would mimic a real broadcast.

Those provided useful, transitional snapshots, but Raimi still needed live fans in seats once actors took the field. With a combination of radio calls, newspaper announcements and traditional apartment fliers, the film crew rounded up anywhere from 300 to 1,200 local extras each day to show up to Yankee Stadium over a month’s time.

“It was quite a zoo just bringing in that many people who were not normal paying customers,” Bozman says.

It was impossible to bring a sellout crowd into the park each day, so assistant director Stacey Beneville would coordinate with Raimi or Ferguson and move large groups of extras to fill certain sections based on the width of the shot, often using more trained background actors to sit around home plate and the dugouts. The crew also used cardboard cutouts to line the backs of sections, “and from a distance, in a long shot, you just see people,” Beneville says. When he wasn’t shooting, Ferguson would hold up large cue cards and conduct fans to cheer or boo depending on the necessary crowd response. “I had the extras in my pocket,” he says.

Raimi’s crew kept a detailed log of scenes that could be filmed in the morning and those that had to wait for the afternoon, to maintain continuity as the late fall shadows crept in. “There’d be 800 people, and then we’d say, ‘All right everybody here, move to the third-base side and fill that up,’” Bozman says. Beneville led the Bronx masses with a megaphone, dressing fans with T-shirts over their coats and occasionally rounding up stragglers. “It’s like a cattle drive. After a certain point, people know where they’re going,” she says. The studio eventually used some of its budget on computer-generated fans to fill in the remaining gaps.

Still, to have homegrown Yankees fans fill parts of the Stadium and provide their own hostility was invaluable, and for some actors in Tigers uniforms, unnerving. “To have real fans in the stands reacting like he was the other team was very upsetting,” Beneville recalls one prominent actor saying to her. But she told him: “This is what it’s like to be a professional ballplayer and not be [on] the home team.”

In between filming and the movie’s release on Sept. 17, 1999, Yankees starter David Cone threw a perfect game on the same mound Costner toed months earlier. The possibility of a veteran finding perfection at the sunset of his career suddenly wasn’t so far-fetched. “What it did was underscore that the scenario we put forth actually could happen,” Costner told Yankees Magazine after the movie opened.

For Bozman and the rest of the crew, filming inside Yankee Stadium continues to be a cherished memory, especially the “awe-inspiring experience” of walking to the mound and running the bases. As a New Yorker who continues to attend baseball games, Ferguson says that he -- or at least his distinctive voice -- still gets identified as that obnoxious Yankees fan, spitting venom at Chapel and the Tigers.

“This is 20 years later. How does this happen?” Ferguson says, before answering his own question. “It’s kind of an iconic Yankees movie now.”