His dance classes, no shock, were a sardine sweatbox. If Nathaniel Hackett can get 40 strangers grooving in sync to Justin Timberlake, then surely, you plead to David Schrag, surely he can beat the Chiefs.

“The one thing about him is, he’s just so completely fearless,” Schrag, one of Hackett’s old pals and a fellow UC Davis alum, told me in advance of the Broncos’ season-opener Monday in Seattle.

“He was never afraid to be goofy and be funny. But also, he learned really quickly, too.”

Every week, whenever a young Hackett put on that little headset and started stretching on that little platform, it was as if someone had popped a champagne cork inside the Aggies’ Activities and Recreation Center.

Broncos defensive coordinator Ejiro Evero dropped in on some of those hip-hop classes Hackett taught on campus 20 years ago, but joked that he burned the tapes. Schrag remembered some 30-40 people crammed into a corner of the room, hips swaying in time the way rows of wheat wave in the morning breeze, hanging on Nathaniel’s every word.

We ready?

Let’s do this!

“His classes were huge, and here was this big football-player guy teaching dance classes to dozens and dozens of students,” Schrag recalled with a laugh. “And I think that was mainly because — he’s a good dancer, absolutely — it was just his personality. He was just very charming. He owned the room. People loved being around him.”

Love that energy!

Work it!

“He’s always going to be that super-excited 14-year-old,” said Schrag, an elementary school administrator in northern California by day and dance instructor at night, about the Broncos’ first-year coach.

“It’s like, ‘Hey, guys, what are you doing?’ Just always positive and upbeat and outgoing.

“He wins people over very quickly. He’s got a very, very strong natural presence and charm. Obviously, he’s used that in his coaching life.”

Yeah, just a little.

Schrag hit Nathaniel’s orbit when he became roomies with Hackett’s older brother David. He’d occasionally visit the Hackett family in Kansas City when their father, Paul, was an assistant with the Chiefs, and when Nathaniel was the classic, tag-along little brother. The three would sometimes huddle up to catch the latest music videos of their favorite hip-hop and R&B acts, then go out and try and mimic their dance routines.

“We thought we were cool,” Schrag laughed. “Way cooler than we usually were.”

You can’t fake cool. Whether it’s a dance class or an NFL locker room, the audience can spot phony cool from a mile out.

“I mean, you look at what we do, and we’re choreographing 11 guys throughout every single play,” Hackett explained to me after practice late last week. “And there’s a little bit more reaction in everything that you’re doing (in football).

“But a perfectly-executed play, it looks like a dance — from the rhythm of the quarterback going back in the pocket, to hitching up, to being able to time it perfectly with a wide receiver’s route, and that delivery of the ball.

“I mean, I remember my dad would always talk about Joe Montana, saying that he was one of the best dancers in the world, just being able to be back there and all the timing (that it took).”

Nate Lasso is a lot of things. He’s green. He’s amped. Jab a set of jumper cables his ears, and he’d probably bring the original battery inside a ’73 Pinto back to life.

But bogus?

Bogus, the new Broncos coach is not.

“He tried to do one (move) in practice,” wideout Courtland Sutton recalled with a grin. “It didn’t go very well.

“He said he could do it, though. I mean, if you’re teaching a hip-hop class, you’ve got to be able to do something.”

Schrag can’t promise Broncos Country a playoff berth right out of the gate. Or a division title in the viper den that’s doubling as the AFC West.

But he will say this: For this guy, they’ll run through six brick walls trying.

If Hackett can command UCHealth Training Center the way he used to command those dancing fools back in Davis, the Broncos’ glasses will never feel short of half-full. No matter how much blood, sweat or tears get spilled along the way.

“Especially with dancing, if you’re afraid to just get out there and own it, you’re already (sunk),” Schrag said, laughing again. “He had the moves. He definitely is legit.”

Once the curtain goes up Monday night, we’re all about to find out just how much. On this stage, the first step is always the bravest.