To grasp how high Sheldon Richardson’s stock is rising as a Viking in December 2018 one must understand how low it fell as a Jet on July 31, 2015.

The headline in the New York Daily News that day screamed, “Big Apple Idiots.” The first sentence asked, “Who’s New York’s dumbest athlete?”

“Me and Jason Pierre-Paul were on there,” said Richardson, referring to the then-Giants defensive end who mangled his right hand with a firecracker. “I got ranked ahead of JPP. Said I was dumber than him blowing his fingers off. Harsh. But, hey, what’s New York without drama?”

Richardson turned 28 Thursday. He’s in a good spot as the happy, focused father of 2-year-old Riley Rose Richardson. He’s also one of coach Mike Zimmer’s most coveted type of player — rarely found three-technique D-tackles with quick-twitch, high motor and 300-pound frame. And he’s also the guy who sacked Aaron Rodgers twice in last week’s win over the Packers and heads to New England on Sunday with 2 ½ career sacks of Tom Brady.

But the first part of 2015 was a darker time for Richardson. The murder of childhood friend Dorance Harvey had him in a bad spot mentally. To the point where “I just kind of fell off the wagon a little bit.”

A positive test for marijuana earned him a four-game suspension. Then, within hours of Richardson reporting to training camp, apologizing to teammates and telling reporters the Jets wouldn’t have to worry about his name being in the news again, a Missouri prosecutor announced details and charges in an incident earlier that month that started as a 143-mph road race with another car and ended with Richardson being arrested at gunpoint.

So, what would 28-year-old Sheldon say to 24-year-old Sheldon if he could?

“I’d punch him in the back of the head,” Richardson said. “For real. Just wake up, kid. Life is bigger than you and your feelings. Honestly, I brought all of this on myself.”

Richardson has been paying down a debt for those two incidents ever since.

He was suspended without pay for five games over two years and “then they took about half of my $5 million signing bonus,” he said. Then he got traded to Seattle before last season and got lowballed by the Seahawks after last season because, he believes, they knew he’d have a harder time getting a lucrative multiyear deal from a team unfamiliar with him.

They were right. He had baggage but only 1 ½ sacks in two years after posting 16 in his first three years as the 13th overall pick in 2013, the NFL Defensive Rookie of the Year and a 2014 Pro Bowler.

The Vikings offered $8 million with $3 million more in incentives for one “prove-it” year. Defensive line coach Andre Patterson laid down the ground rules ahead of time and told him “not to come here if he couldn’t abide by them.”

“I guess my concerns were he’s been with three teams in three years,” Zimmer said. “That’s always kind of a concern. I think he had some things with the Jets that weren’t real positive. But since he’s been here, he’s been real good as far as studying in the meetings, paying attention and trying to do everything exactly how we’ve asked.”

Can he be trusted with a long-term deal?

“From what I’ve seen, yeah,” Zimmer said. “But you never know when guys get big contracts or whatever.”

‘It was a party’

Born and raised in St. Louis, Richardson left the University of Missouri after his junior year. He was 22 heading to the Big Apple.

“Me being a Midwest kid going to the East Coast, that was a party,” Richardson said. “And I abused it a little bit. But I also gave those people 120 percent of all my efforts.”

Former Jets coach Rex Ryan, who coached Richardson in his first two seasons, agrees with that last part.

“He’s a heck of a young man, and, outside of Aaron Donald, he’s right up there with the rest of the best at that position,” Ryan said. “I never had a single issue with him. It makes perfect sense for him to be in Minnesota long-term.

“Guys make mistakes. That’s just the way it is. We’ve all made them. The guy who’s squeaky clean and never had an issue in his life is few and far between. Sheldon wasn’t perfect, but he’s grown from his experiences.”

Asked what triggered his problems in early 2015, Richardson cut loose, calling himself “an open book.”

“With the marijuana thing, I already had a diluted test result before, so I was put in the program,” he said. “Dorance’s death hit me hard. It’s still tough.”

Harvey, 23 at the time, was killed inside his car in St. Louis in a yet-unsolved shooting. Richardson had just dropped him off at his car 30 minutes before getting the call that he had been shot.

“When that happened, I just fell off the wagon a little bit,” he said. “I didn’t care. I didn’t see myself as a public figure. Back then, I didn’t really know my responsibility to my platform. I disrespected my platform and learned a lesson the hard way.”

Richardson says he didn’t leave his house for months. When he did, he hopped in his $200,000 Bentley Flying Spur four-door sport edition with two other men and a 12-year-old. They went racing.

“I thought everybody drove fast,” Richardson said of his 143-mph clocking on Interstate 64 around midnight.

He had a loaded handgun in the front seat.

“It was registered,” he said. “It’s protection. I live in St. Louis.”

Richardson initially refused to pull over. He turned off his lights, went through a red light and pulled into a driveway.

“One thing just led to another,” he said. “It was fun until it ended at gunpoint.”

According to the police report, the car smelled of marijuana. But no drug or gun charges were filed. Richardson was found guilty of reckless driving and resisting arrest.

Motivating factors

So if indeed Richardson has turned his life around, what was the turning point?

He cites two of them.

He showed off the first one when Riley Rose sang happy birthday to him via FaceTime from Los Angeles in the TCO Performance Center locker room on Thursday.

“I’m trying to make as much money as possible so she can be comfortable,” Richardson said. “And I don’t want her making the same mistakes Daddy did.”

The other turning point?

“I still wanted to be great,” he said. “This is who I am. I abused the NFL shield a little bit, and I’ll never do it again. It’s just as simple as that. I love football.”

Besides doing everything he’s asked to do, Richardson has been, according to Patterson, exactly what the Vikings needed in a three-technique tackle. Not only is he tied for second on the team in sacks with 3 ½, but he’s also played a “major role” in end Danielle Hunter’s 11 ½-sack season, as well as the team ranking second in sacks per pass attempt (10.1).

“Last year, we started off hot in sacks, but then the production kind of went down toward the end,” Patterson said. “I saw where people wrote that it was because we ran out of steam. That had nothing to do with it. Teams changed the way they were blocking us, and the quarterback sat shallower in the pocket.

“We needed an inside push. We needed somebody to make the quarterback stay high in the pocket and give the ends a chance to turn the corner. Sheldon has been that guy.”

Richardson said he wants to finish his career as a Viking. He enjoys his teammates, respects his coaches and appreciates that, “Nobody is babying nobody around here because of their paycheck. You’re held accountable like you’re a practice squad guy.”

So what kind of contract will it take to re-sign with the Vikings?

“One that’s respected,” Richardson said. “I feel like offenses are blocking me as if I’m one of the top-paid guys in the league. So I feel like I need to prove that first. I know I’m not proving it. The team says I’m doing great, but I feel I need to be more productive.”

But more sacks wouldn’t necessarily mean Richardson would be doing his job better. It’s a team game requiring gap responsibilities and respect for the running game.

“I could easily sell out my teammates and go chase more sacks,” Richardson said. “I choose not to. I got a chance to make $11 million with incentives, but I’m playing the run and making sure I do everything right to win ballgames and make a playoff run before we start talking contracts.

“I’ll cross that bridge when it comes. I haven’t talked to [General Manager] Rick [Spielman]. So I don’t know what the future holds. They say they’re happy with me. When we talk about dollars, we’ll see.”

Ryan, for one, is pulling for someone he calls a fellow “Big Apple Idiot.”

“Believe me, whatever they called Sheldon in New York, they called me a billion times worse,” Ryan said. “Sometimes, you take that with a grain of salt, move on and try to become the better person. The great thing is that’s what Sheldon has done.”