For the first time since he started coaching football at his high school alma mater in 1979, Vic Fangio will be an observer this fall, choosing to collect the final year of his Broncos contract instead of pursuing a defensive coordinator post.

But Fangio’s presence will be felt throughout the NFL.

“Vic’s imprint is probably 25% of the league, right?” Broncos defensive backs coach Christian Parker said.

Slightly more, actually.

Playing “Six Degrees of Vic,” the coach and/or defensive coordinator of six teams have a direct connection to Fangio: Coaches Brandon Staley of the Los Angeles Chargers (worked for Fangio in Chicago and the Broncos) and Robert Saleh of the New York Jets (Houston) and four defensive coordinators — the Broncos’ Ejiro Evero (San Francisco), Minnesota’s Ed Donatell (San Francisco, Chicago and the Broncos), Seattle’s Clint Hurtt (Chicago) and Detroit’s Aaron Glenn (played for Fangio in Houston).

A second degree produces three more coordinators: Green Bay’s Joe Barry (worked for Staley with the Los Angeles Rams) and two coaches who worked under Saleh with the 49ers — Cleveland’s Joe Woods and the 49ers’ DeMeco Ryans.

Add it up and that is 28.1% of the league.

“It’s a copy-cat league and when you have success, people look at it,” said Tony Dungy, the Pro Football Hall of Fame coach who works for NBC. “(Coaches) study tape and they take the good things and they take the principles from it. Coach Fangio has had success with a number of franchises and those principles are good.”

So why is the defense that Fangio inherited from Dom Capers (now a Broncos assistant coach) and added layer upon layer to it over the years so useful?

General manager George Paton: “It’s just hard on quarterbacks with the disguises, the two-high (safety) coverage. It’s also hard on quarterbacks if you’re good up front and can stop the run.”

Defensive line coach Marcus Dixon: “You can be multiple in your coverages and multiple in your front structures. And it allows you to put your best players in the best positions to make plays.”

Inside linebackers coach Peter Hansen: “You need to have extreme talent to be successful in a ‘Cover 3.’ When Seattle was really rolling, every position was talented. Obviously, it’s a talent-driven league, but there have been some years when medium talent with Vic and Dom and it still had success.”

In summation: The five-man front helps defend the run. … Inside linebackers are often “clean” to make plays. … The pre-snap disguise includes playing one type of zone coverage apiece on each half of the field.

Evero, in his first NFL coordinator opportunity, will be tasked with inheriting the personnel Fangio helped acquire from 2019-21 and putting his stamp on the system to provide better results.

“There are definitely a lot of variations we want to do, both very small and on a major scale,” Parker said.

Those changes, if they can be deciphered by the untrained eye, will be on display Monday night in Seattle.

Will the Broncos pressure more? They rushed five or more on 26.2% of the opponent’s drop-backs last year, per The Denver Post’s game charting.

Will edge rushers Bradley Chubb and Randy Gregory be stationed as interior rushers? This should be a premium third-down look to match both players against a guard or center.

Will they travel cornerback Pat Surtain II with an opponent’s top receiver? Evero joined the Broncos from the Rams, where coordinator Raheem Morris moved Jalen Ramsey around the field.

Will their sub-package plan include more dime (six defensive backs) than nickel (five)? Last year, the Broncos used dime personnel 16 times against Washington, 18 at Dallas and 27 in the first Chargers game.

And will they be able to stop the run better? The Broncos finished 15th in rush defense last year.

It all starts with the run game and to that end, the Fangio scheme prioritizes bodies at the line of scrimmage.

“As soon as you take five guys and put them at the line and two of them are really big, physical guys on the edge, you’re immediately creating 1-on-1 blocks for the offense and making it harder for them to work to the next level or work on double teams,” Broncos outside linebackers coach Bert Watts said.

In the Broncos’ base scheme, that will be Chubb and Gregory outside and a defensive line of D.J. Jones, Dre’Mont Jones and DeShawn Williams.

The idea is to clog up the gaps and allow inside linebackers Josey Jewell and Jonas Griffith to roam free.

“In other schemes, you have a specific gap to cover, but in this scheme, you fly around, flow to the football and you use athleticism,” Griffith said. “You can move east-west and then when you see the play, you can trigger.”

If the Broncos can stop the run, that will open up the playbook for Evero on third down.

“You can get exotic on third down and change your front look and your back-end disguise,” Dixon said. “You’re not sitting ducks.”

The Broncos were a dreadful 28th last year on third down (opponents converted at 44.9%) and one of the issues was too many third-and-shorts. Opponents had 75 plays when they needed 1-3 yards (50 conversions, 66.7%).

Needing 4-7 yards, opponents were 36 of 81 (44.4%) and needing 8 or more yards, they were 15 of 69 (21.7%).

The Fangio scheme has usually run a two-safety shell, but teams use that as a disguise, such as rolling a safety into coverage while the cornerback blitzes.

After a soft opening of quarterbacks (Seattle’s Geno Smith, Houston’s Davis Mills and San Francisco’s Trey Lance), the Broncos’ defense better be on-point in October when they face Las Vegas’ Derek Carr, Indianapolis’ Matt Ryan and the Chargers’ Justin Herbert in consecutive games.

“It all comes down to personnel and how you do things,” Dungy said. “A scheme that works is (about) getting players to play and that’s the beauty of coaching.”