NBC's "Saturday Night Live" seems like it's been part of the entertainment firmament forever. The brainchild of Canadian comedy writer Lorne Michaels kicked off nearly a half-century ago, and yet improbably remains a consistent provider of laughs, controversy and rising stars.

But how did it all start? That's the focus of "Saturday Night" (in wide release Friday), director Jason Reitman's gloriously frenetic version of the 90-minute span before the first episode aired live on Oct. 11, 1975.

"It's just about a group of people trying to totally revolutionize TV in 90 minutes," Reitman says with a laugh.

Reitman's movie plays like a comedy freight train just barely staying on the tracks, complete with crashing light rigs, pouting stars, sudden brawls and even an appearance by Milton Berle's famously outsized member.

There's no question that Michaels was fomenting nothing short of a genre-bending explosion in Studio 8H. But the high jinks seem so improbable that it's fair to ask just how much of "Saturday Night" really happened on that fall night at New York's Rockefeller Center.

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USA TODAY fact-checked some of the movie's more outrageous scenes with the help of Reitman as well as stars Gabriel LaBelle (who plays Michaels) and Cory Michael Smith (Chevy Chase).

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Did Chevy Chase and John Belushi come to blows just before the debut of 'Saturday Night Live'?

"Saturday Night" depicts Chase and soon-to-be comedy icon John Belushi (Matt Wood) as two sharks about to rip each other apart just before showtime. And finally, they do come to blows and have to be pulled apart. But the fight never happened that night.

"Jason fictionalized that as a manifestation of the tension that's there, but it's also a reference to the fight Chevy famously had with Bill Murray when Chevy, who'd left 'SNL' after the first year, came back to host in year two," says Smith. "It was an homage to that moment."

Did a lighting rig really come crashing down on the Not Ready for Primetime Players?

No, says Reitman, although "the story we heard was that their famous camera crane, the so-called Chapman Crane that someone would actually ride, lost its brakes and plowed through the set."

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Did John Belushi really balk at signing his NBC contract until showtime?

Yes, says Reitman. "He was nowhere to be found and refused to sign it until the very end. But, adds Reitman, "the point of showing that in the movie wasn't about highlighting a contract dispute but to show how afraid he was about becoming a big star. John was aware of his own genius, but he feared things would get out of control if he became popular on TV."

After leaving "SNL" to pursue movies, including his breakout role in 1978's "Animal House," Belushi died of a drug overdose at age 32 in 1982 at the Chateau Marmont in West Hollywood, California.

Was Billy Crystal a part of the original 'Saturday Night Live' cast?

Yes. The comedian was slated to be a part of the first show but as depicted in "Saturday Night," his bit never made it on air and he eventually left, only to return as a very successful cast member during the 1984-85 season.

Did Johnny Carson berate Lorne Michaels on the phone just before showtime?

"That's true," says Reitman of the late-night host's call to the upstart producer. As "Saturday Night" explains, "SNL" took over the timeslot that was reserved for reruns of Carson's "Tonight Show," and he wasn't thrilled to give it up.

"It might not have happened that night, but Carson had all these rules he put in place to make things hard for Lorne," says Reitman. "The message really was, 'Stay out of Burbank,'" the "Tonight Show"'s home base.

Adds LaBelle: "My sense of it was that they (NBC) didn't respect Lorne at all, they saw him as this hippie. So they were all always at each others' throats."

Did Milton Berle really expose himself to Chevy Chase's girlfriend backstage?

No. The famous comedian, known as Mr. Television, wasn't on the set that night, or, as depicted, taping an old-school variety show next door. (Berle did host "SNL" once, in 1979.) But a scene where he exposes himself has roots in real life.

Berle was "notorious for showing (his penis) to people, so many people have stories of that happening to them," says Reitman, who adds that the scene in "Saturday Night" in which Berle hits on Chase's girlfriend and then insults the young comedian by pulling out his penis is really about the generational clash of comedy cultures.

Was Chevy Chase really handed the reins of Weekend Update at the last minute?

In "Saturday Night," Lorne Michaels gives a terse reading of fake-news headlines during a rehearsal for the show's Weekend Update segment. Michaels then abruptly tells Chase that he should do the job instead. Chase soon became famous for that bit, often opening with his classic line, "Good evening, I'm Chevy Chase. And you're not."

In truth, Michaels was going to take on that task, but long before the first episode handed it to Chase, who originally had been hired as a writer. (Reitman says Michaels and Chase met while both were standing in line to see the 1975 film, "Monty Python and the Holy Grail.") "SNL" is referred to in "Saturday Night" as the "American Python.".