By Dan Durkin-

(CBS) With few exceptions, being an NFL head coach is a thankless proposition.

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The same person in who is introduced as the team’s savior is eventually fired just a few years later and blamed for not fulfilling what were all along empty promises. Since the year 2000, 145 different coaches have been cycled in and out of 32 cities.

For some, despite exhibiting proven success and qualifications, the opportunity to eventually be fired never comes to pass. That almost was the case for Vikings coach Mike Zimmer. After being passed over by the Tennessee Titans, Zimmer was slightly jaded about the process and almost didn’t go for his second interview with the Minnesota Vikings.

“You always hope for the opportunity, but I’m happy with the things I’ve done, the players I’ve had,” Zimmer said. “I guess you wonder sometimes when you see other people get jobs and you don’t get them — I guess that’s when you think that the possibility might not happen.”

Zimmer did in fact go for the second interview with the Vikings and was hired last January to replace Leslie Frazier to become the team’s fifth head coach since 2000.

Some suspected general manager Rick Spielman wouldn’t survive the Vikings’ 5-10-1 season in 2013, but he did. The Vikings followed suit with the en vogue approach, simultaneously pushing reset on both the head coach and quarterback as the team traded back into the first round this past May to select Louisville’s Teddy Bridgewater.

With Matt Cassel signing a two-year deal back in March, the Vikings’ approach was to bring along Bridgewater slowly. However, Cassel broke his foot in Week 2, forcing Bridgewater into action.

Offensive coordinator Norv Turner is a disciple of the Air Coryell scheme, which is predicated on timing and stretching a defense vertically. Quarterbacks are asked to quickly read the field from high-to-low and without hesitation get the ball out to the open receiver.

To ease Bridgewater in, Turner has wisely simplified his scheme. Many of Bridgewater’s passes come off of play-action and zone-read packages, which cut the field in half and make for easier reads in his progression.

Turner’s route combinations typically feature a vertical stretch to either function as a clear-out or a go route to quickly stack on top of the cornerback. At times, Bridgewater has struggled with his deep ball accuracy, looking more like a thrower than a passer.

In theory, receiver Cordarrelle Patterson fills the size-to-speed receiver in Turner’s offense, but he has yet to find chemistry with Bridgewater. Veteran Greg Jennings is still a reliable route runner but lacks the ability to stack and get vertical as he did in his prime with Green Bay.

Tight end Kyle Rudolph has been dealing with a sports hernia but is expected to play Sunday. The Vikings use a lot of 11 personnel, and Rudolph can be used as the move tight end to work the vertical seam.

In combination with a passing game that spreads and stretches a defense out vertically, Turner deploys a power running scheme with leads and counter. As linebackers start to cheat backward to try and get into their coverage drops quicker, a power running game is a natural complement.

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Turner frequently uses pulling guards and physical fullbacks as lead blockers at the second level to create defined running lanes for a running back, which was a perfect fit for Adrian Peterson. Child abuse charges have landed Peterson on indefinite suspension.

The power back role is now handled by Matt Asiata, who runs behind fullback Jerome Felton. Asiata isn’t an elusive runner, rather a north-and-south grinder who has been effective in short-yardage and the red-zone situations.

Anther aspect of Turner’s offense requires a scat back who can be a change-of-pace runner and receiver. That role has been filled by rookie Jerick McKinnon, who is averaging five yards per touch. McKinnon has an explosive first step and can quickly get to full speed.

As is the case with most teams led by rookie quarterbacks, the Vikings offense is struggling to move the ball consistently and put points on the board. Bridgewater has been unable to keep teams honest with his arm.

Defensively, it’s an entirely different story for the Vikings. The days of Frazier’s static fronts with zone looks behind it are long gone.

Zimmer made a name for himself as as defensive coordinator, and he has the young core of Vikings defenders playing fast. As was the case with Zimmer in Cincinnati, Minnesota has a versatile group of defensive linemen who can win single matchups.

Zimmer’s fond of using his linebackers both inside and outside to create presnap confusion in protection schemes. Unlike teams who mug the A-gap and frequently drop their linebackers, the Vikings frequently send the linebackers, then cross them up and use them in stunts and games with the defensive lineman.

Second-year defensive tackle Sharrif Floyd is emerging as one of the league’s premier young three-techniques. Floyd possesses explosive first-step quickness to shoot gaps and command extra attention. In turn, he requires extra help, which creates singles on the edge.

On the edge, the investment the Vikings made in defensive end Everson Griffen is paying off. His nine sacks are the fifth-highest total in the league. Griffen is a tremendous athlete who converts speed to power and quickly bends the edge.

Rookie Anthony Barr has been one of the team’s best weapons, playing responsibly against the run, in pass coverage and as a rusher. Barr was a 3-4 outside linebacker in college but is playing the strong-side backer with violent hands and quick feet.

The secondary is led by free safety Harrison Smith, who has been reliable in pass coverage and has improved as a run defender in both read-and-reaction and tackling.

As they enter Sunday’s matchup with the Bears, the Vikings (4-5) are building a foundation on defense through the draft. Bringing in Zimmer was a wise move to properly architect these young pieces. Looking ahead, their focus has to be on properly developing Bridgewater, which will involve acquiring more weapons and better protection up front.

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Dan Durkin covers the Bears for CBSChicago.com and is a frequent contributor to 670 The Score. Follow him on Twitter at @djdurkin.