Almost nobody behind "Uncut Gems," the Adam Sandler/Kevin Garnett drama steeped in NBA lore that opens Friday in New York and Los Angeles (and nationwide on Christmas), wanted the movie to have anything to do with Garnett and the Boston Celtics -- unless it somehow involved the Celtics' humiliation.

Josh and Benny Safdie, the writer-director brothers, are diehard fans of the New York Knicks -- which naturally means they hate the Celtics. "I hated Boston," Josh Safdie told ESPN this week. "I hated KG."

Sandler was born in Brooklyn, but his family moved to Manchester, New Hampshire -- prime Celtics country -- when he was 5. Sandler had a chance to leave the Knicks behind and jump onto the Boston bandwagon years before Larry Bird, Robert Parish, and Kevin McHale formed the Big Three.

"I could have become a Celtic fan," Sandler told a small group of reporters in New York last week. "But I rooted against Larry Bird very hard. I wanted Julius [Erving to win]. I wanted the Sixers. I don't know what was with me. I made a mistake."

The NBA's lottery system has corrupted Sandler's New York fandom, he told the group. "I'm almost madder when [the Knicks] win," he said.

When the Safdies began writing "Uncut Gems" a decade ago, they did so with Amar'e Stoudemire in mind for the role of the NBA star who improbably comes into the orbit of the stressed-out, stretched-thin, gambling-addicted Diamond District jeweler played by Sandler. Sandler's character, Howard Ratner, acquires a black opal mined from Ethiopia. Garnett visits Sandler's shop in New York during the Celtics' playoff series against the Philadelphia 76ers in 2012 and becomes fascinated with the opal, believing it has mystical powers that help him play better. With that knowledge, Sandler's character begins betting on the series.

The film includes snippets of real footage from that series. The league did not license the footage, sources say; the Safdies will claim fair use if necessary.

The Safdies are Jewish, and the intersection of basketball and New York City Jewish culture runs through the movie. Stoudemire has traveled to Israel many times to trace his Jewish roots and develop his faith, first in 2010. He later played in Israel and discussed plans to convert to Judaism, and this year he was granted Israeli citizenship. He also played five seasons for the Knicks. The Safdies thought he was a natural fit.

Their agents pressured them to aim higher -- perhaps as high as Kobe Bryant. They spent two weeks reorienting the script around Bryant's 61-point game at Madison Square Garden in February 2009. Then they learned Bryant wished to direct films, not act in them.

"I was like, 'F---! I just spent all this time rewriting!'" Josh Safdie said. "In the end, it's fine. I didn't want to make a Laker movie. I definitely didn't want to make a Celtic movie, either."

(Bryant told ESPN he had never heard this story before. He was never attached in any formal way, and never saw a script. The Safdies never met or spoke to Bryant.)

They moved on to Joel Embiid, but working around the schedule of an active player proved impossible. The studio gave them a list of retired players. They met with a few, including Chris Bosh, Josh Safdie said. Garnett's name was on the list, too. They cringed.

They agreed to meet with Garnett anyway. Garnett's representatives told them they would have an hour. The meeting lasted three hours. Garnett regaled them with stories. He was different in person than he was on television and in media interviews.

"I would always watch KG postgame because he was so entertaining," Josh Safdie told ESPN. "But I realized after meeting him that I didn't know his real voice. I had to learn that voice. He's eloquent. He's a great storyteller. I wrote for that voice. And he worked really hard."

Garnett plays himself, and the role is huge. It is not a cameo. He is perhaps the second-most important presence, behind only Sandler. He is (in this amateur critic's opinion) quite good -- charismatic, funny, intimidating when the part calls for it.

"Acting is preparation, just like anything else," Garnett told the group in New York. "I didn't want to fail them. They took a risk on me. When I showed up to set, I was ready. It took me back to, 'OK, it's Rasheed Wallace tonight. It's Tim Duncan tonight' -- watching film. I took those same things coming in here."

"He took his lines very seriously," Josh Safdie told ESPN. "He added a lot of flair, too. He improvised a bit, but he stuck mostly to the script."

At a private screening this week for the Celtics, Wyc Grousbeck, the Celtics governor, told the Safdies that Garnett -- superstitious and ritualistic -- was the right choice. "There is some supernatural power inside KG, and the idea it would come from a gem is perfect and believable," Grousbeck told ESPN.

The movie is littered with NBA references. Here are the stories behind some of them.

• There are, as you might expect, several references to the Knicks and to the misery of being a Knicks fan. The events of the movie come only months after Linsanity. One character laments Jeremy Lin will leave in free agency because "Dolan ruins" everything, a reference to Knicks owner James Dolan. The actor improvised that line, Josh Safdie said.

"Linsanity was the greatest gift ever given to this city," Josh Safdie told the New York roundtable with a heavy sigh.

"It was a hellfire run, dog," Garnett agreed.

• As has been reported elsewhere, Garnett told the group he was not surprised Kyrie Irving left the Celtics. "You gotta have some major cojones to be [in Boston]," Garnett said. Garnett was surprised Irving and Kevin Durant chose the Brooklyn Nets.

"I thought they should have [gone to] the Knicks." Garnett told the group. "I'm not a Knicks fan by far, But to come into this city and dominate, man, the first superstar to hit New York and be vibing is going to be bigger than life. Remember I said that."

I then asked Garnett if (in theory) he would have signed with New York alone, or made his signing contingent on the Knicks pairing him with another star. "You gotta come with pieces, man," Garnett said. "I didn't think they put superstars around [Carmelo Anthony]. They have the pocketbook to bring players here, but for some reason, they haven't put it together."

Why? "I wish I knew so I could go up there and say, 'I got a plan!'" Garnett told the group. "Pretty much anybody's looking at [former Knicks president] Phil Jackson like, 'S---, I coulda did what he did!'"

• There are two championship rings featured in the movie: a 1973 Knicks ring (worn by Ratner) and Garnett's 2008 ring. Both are replicas, Josh Safdie told ESPN. Garnett told the roundtable he does not wear his ring. He lives by this rule: "You can only wear one if you got two."

• When Sandler's character first meets Garnett, he peppers Garnett with random NBA questions. One of them: Who would win in a fight between Ben Wallace and Tony Allen? Garnett's answer: "TA, all day!"

Sandler improvised the Allen-or-Wallace question during rehearsal, and the Safdies liked it so much they put it into the script, Josh Safdie said. Allen learned recently he was name-dropped in the movie, but he did not know the context until ESPN contacted him this week.

"It's really cool," Allen, Garnett's teammate for three seasons in Boston, told ESPN. "I'm hyped. You just made me smile. Yo, I'm in a movie!"

As for the theoretical fight, "You know I don't want no smoke with Ben Wallace," Allen said. "He scared me, trust and believe that. That's just KG repping his boy."

• The Safdies organized a private screening for the Memphis Grizzlies. To their delight, Ja Morant later sent them an autographed jersey with a message, "To Josh and Benny, much love," Josh Safdie said. "You know how cool that jersey is gonna be in 10 years?" Safdie added. Allen sent them an autographed ball.

• During one dinner scene, several characters have an argument about whether Chris Paul is overrated. (Josh Ostrovsky, otherwise known as The Fat Jew -- an internet celebrity and NBA superfan -- is an extra in that scene, Josh Safdie said.)

One character defends Paul, listing the All-Star and All-NBA honors Paul had accrued by 2012. The Safdies chose Paul as the subject of the debate because they were writing the script during Paul's trade from the New Orleans Hornets to the Los Angeles Clippers.

"It stems from all the hype around Lob City," Josh Safdie said.

In the original script, the argument extends longer, with one character pointing to Paul's achievements in the Olympics, Josh Safdie said. "They don't count," another character scoffs. They trimmed that in the final cut.

Paul declined comment through an Oklahoma City Thunder representative, saying he had not yet seen the movie.

• One person was not surprised by Garnett's acting skill: Doc Rivers, the current Clippers coach and former Celtics coach who recorded a voiceover for the film. Rivers built an out-of-timeout play around Garnett's acting ability, Garnett and Josh Safdie told the roundtable. He instructed Garnett to come out of the huddle acting "really cocky" so the other team would expect the ball to go to him. (The play was designed for Paul Pierce.)

Rivers was Method-serious about Garnett's performance. "Do you know how many times we did this? Garnett recalled. "I messed it up so many times in practice. I done that 100 times because I didn't do it the way he wanted." Garnett would break from the huddle clapping, only for Rivers to tell him, "Clap more!" Garnett said.

• Rivers in the movie is heard giving a pep talk at halftime of Game 7 of the Sixers-Celtics series as the camera zooms on Garnett, sitting at his locker and rolling the titular gem in his hand. "We're like roaches!" Rivers yells. "You can't kill us!"

In real life, Rivers used the "roaches" line last season after his Clippers rallied from 31 points down to beat the Golden State Warriors and even their first-round series 1-1. Rivers told ESPN the Safdies asked him to recycle the speech for the movie.

• Rivers recorded his voiceover during the Clippers' Kawhi Leonard recruitment, the Safdies told the roundtable. He hinted to the Safdies that a second player might be involved, but he did not tell them who it was. "We didn't realize it was Paul George," Josh Safdie said. "That's crazy!"

• Boy, were the 2012 Eastern Conference playoffs weird. Chicago was the top seed, and expected to trounce Philly in the first round. Then Derrick Rose tore his ACL late in Game 1. The Sixers won in six, setting up the second-round series against Boston.

It was a seven-game bloodbath. Philly did not crack 100 points once. Boston managed to twice. Boston won the decisive Game 7, 85-75. Pierce fouled out with 4:16 remaining and Boston up by only three. Rajon Rondo drained a foot-on-the-line 2 and a 3-pointer -- just his second of the series -- in the last three minutes to give Boston a 10-point cushion.

The aging Celtics then somehow won Games 3, 4 and 5 over the Heat in the conference finals to take a 3-2 series lead. LeBron James responded with perhaps the greatest and most consequential game of his career in Game 6 in Boston -- a 45-point, 19-of-26 masterpiece. Miami grinded out Game 7, with LeBron driving around and through Brandon Bass. (I swear this is a thing that happened.)

• Before Game 7 of Philly-Boston in the movie, Ratner (Sandler's character) implores Garnett to "step on Elton Brand's f---ing neck." (Brand was a member of that Sixers team.) Brand attended a screening in New York. "I cringed," Brand, now the GM of the Sixers, told ESPN. "I care about my neck."

"I was rooting for myself the entire movie," Brand said. "They were showing KG hitting all those midrange jumpers in my face, and I just kept hoping in the movie they would let us win. I was there. I know what happened. That's when you know a movie is good -- when it transports you."

• Brand is still salty about those Rondo jumpers. "When Paul fouled out, I was thinking, 'This is our game,'" Brand said. The Heat had eliminated Philly, 4-1, in the first round the season before. The Sixers wanted another shot. Brand still wonders if ownership would have kept that Sixers team together had they advanced to the conference finals. In August 2012, the Sixers acquired Andrew Bynum as part of the four-team Dwight Howard trade. They also waived Brand that summer using the amnesty provision.

"I get it," Brand said. "I wasn't in management then. You gotta go for championships. The second round isn't enough."

• Upon first meeting Garnett, Ratner asks him if Rivers would be angry to know Garnett was in New York perusing diamonds the morning of a playoff game in Philadelphia. We asked Rivers. "On a game day, I don't know," Rivers told ESPN. "I am actually a big proponent of guys getting out of their hotel rooms. During the Finals, I flew in Ray Allen's golf clubs and had him go golf. But not on a game day."

• Speaking of Ray Allen: Garnett told reporters he did not reach out to Allen for acting advice. (Allen famously starred alongside Denzel Washington in Spike Lee's "He Got Game.") "I haven't really talked to Ray at all," Garnett said.

• Before ESPN contacted him last week, Spencer Hawes, Philly's starting center in 2012, had no idea he plays (by chance) a pivotal role in the movie. Ratner bets on (among many other things) Garnett winning opening tips against ... Hawes. The movie features footage of said tips.

"I was never good at those," Hawes said. "Not much of a leaper." Brad Miller, who played with Hawes in Sacramento, tried to teach Hawes to win tips by subtly nudging one forearm into his opponent as the referee threw the ball up. "I couldn't master the timing," Hawes said.

"I was already planning on seeing the movie, but now I have to," Hawes said. "The only movie I've ever been in is the Teenage Mutant Ninja Turtles sequel, and I don't even know if I made the final cut." (Several members of the 2014-15 Clippers, including Hawes, filmed a basketball scene for that movie, but Hawes is not listed in the IMDB credits.)

• For the record, play-by-play data lists Hawes as going 3-4 on opening tips against Garnett in that 2012 series.

• Rivers' favorite memory of that series was his game-day ritual of walking from morning shootaround in Philadelphia back to the team's hotel with the late Flip Saunders, who worked with the Celtics as a special adviser during those playoffs after the Washington Wizards fired him as coach. One problem: The walk to their Philadelphia hotel was about 5 miles, giving Philly fans plenty of chances to spot Rivers and Saunders.

"Fans started blowing their horns, saying really rude s---," Rivers recalled, laughing. When the Sixers won Game 4 to tie the series at 2-2, it guaranteed a Game 6 in Philly -- and another walk. "Flip was distraught," Rivers said. "I thought it was because of the loss. It was because of the walk. He didn't want to walk again. He was like, 'We needed to win this game, I can't do this walk again.' It is a very fond memory of Flip for me."

• In his first scene, Garnett wears a black leather Starter jacket featuring the logos -- also rendered in black -- of all 30 NBA teams. It is awesome. In planning wardrobe, the Safdies came across a photo of a young, Minnesota-era Garnett wearing a similar jacket. They had their costume designer, Miyako Bellizzi, look for Starter jackets before settling on the black version, Josh Safdie said.

In 2013, the Safdies directed "Lenny Cooke," a documentary about Cooke -- a high school basketball phenom who never panned out. Cooke wore a color version of the same jacket.

ESPN's Ohm Youngmisuk and Nick Friedell contributed reporting to this story.