For five excruciating days last winter, new Chicago Bears coach Matt Nagy was in attack mode.

He recruited Vic Fangio hard to remain the team's defensive coordinator, knowing Fangio was the best candidate to shepherd a rising defense while Nagy rebuilt the Bears' offense. Fangio had other suitors, including the NFC North rival Green Bay Packers, but Nagy sold him on his vision and the value of the foundation he laid in Chicago the previous three seasons. In the meantime, Nagy set his sights on another highly respected assistant coach: offensive-line guru Harry Hiestand, on the staff at Notre Dame at the time.

You know the rest. The Bears rocketed to a division title in Week 15 in part because of Fangio's defense, ranked No. 1 in Football Outsiders DVOA through 15 weeks. And Nagy's creativity revitalized the Bears' offense, with a big if underplayed boost from Hiestand's steady hand.

The annual January coaching carousel, and the breathless reporting that comes with it, can seem overdramatized. But usually it's not difficult to draw a line from those events to December results. The composition and mesh of a coaching staff is among the most underpublicized, if subjective, indicators of long-term success.

"This is actually something that really matters," said Joe Banner, an executive with the Philadelphia Eagles, Atlanta Falcons and Cleveland Browns for two decades. "Say you're a fan, and you're looking at your team after it hired a new coach. If you have an accurate assessment of the coordinators that were hired, you're going to have a good ability to predict how well that coach is going to do, in my opinion. That's how important it is."

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A similar outcome has materialized in Indianapolis, albeit in part by accident after New England Patriots offensive coordinator Josh McDaniels rescinded his commitment to take the head-coaching job. Colts general manager Chris Ballard had signed part of McDaniels' proposed staff to contracts, most notably defensive coordinator Matt Eberflus. By the time the Colts hired Frank Reich -- who, like Nagy, had an offensive background -- options were limited. Reich took Ballard's advice on Eberflus, whom he considered a future star. Eberflus has in turn engineered a massive turnaround of the Colts' defense, raising it 13 spots in DVOA from 2017 to No. 10 this season. The Colts, winners in seven of their past eight games, are in the AFC wild-card race at 8-6.

"Chris was very persuasive and very strong in his conviction that Matt was the right guy," Reich told reporters.

Potential assistant-coach hires are a standard part of head-coach interviews. The conversation offers deep insight into how the candidate thinks and his likelihood for success.

"Who they hire and how well they manage them ends up having a huge amount to do with how successful a head coach is," Banner said. "You can tell everything from how thoroughly they've thought about this, how long they'd been planning for this, how important they think it is from their reaction to the questions. It gives you an insight way beyond just who the coaches are going to be. You're really learning a lot about how [the head-coach candidate] thinks about the game, how they think about being a head coach and what that is."

The randomness of timing also can drive the decisions, with consequences felt for years to come. In 2017, former Jacksonville Jaguars coach Gus Bradley fielded interest from multiple teams to become a defensive coordinator. At least two had new head coaches in the Los Angeles Chargers and San Francisco 49ers.

The Chargers hired Anthony Lynn as their head coach Jan. 13, 2017, while the 49ers were waiting to formalize an agreement with then-Falcons offensive coordinator Kyle Shanahan, who was preparing for Super Bowl LI on Feb. 4. Bradley joined Lynn on Jan. 20.

The Chargers are 20-10 since, in part on the strength of a defense that is ranked No. 12 in DVOA. The 49ers officially hired Shanahan on Feb. 6 and ultimately tapped linebackers coach Robert Saleh as defensive coordinator. In two seasons under that arrangement, the 49ers' defense has ranked No. 28 and No. 25 in DVOA, respectively.

Gus Bradley helped make the Chargers a Super Bowl contender by turning out the defense. AP Photo/Chris Carlson

Bradley was a "name" candidate who has proved worthy of the interest. Just as often, however, teams rush to make reputation-based hires that ultimately scuttle a season.

There wasn't much public backlash last winter in Arizona, for example, when new Cardinals coach Steve Wilks hired Mike McCoy as his offensive coordinator. McCoy had experience as a head coach with the Chargers, had served two stints as the Denver Broncos' offensive coordinator and was a top candidate to be the Cardinals' head coach in 2013.

But McCoy's seven-game tenure was a disaster, and the Cardinals' offense ranked No. 31 in DVOA when he was fired Oct. 19. The Cardinals are 3-11, on track for the No. 1 overall pick in the 2019 draft, and the damage was so severe that Wilks might not make it to a second season.

Longtime NFL general manager Charley Casserly, now an NFL Network analyst, spent time each offseason picking the brains of his colleagues around the league. Looking for names for future searches, Casserly would ask why they decided against hiring certain candidates.

"Invariably," Casserly said, "many of them said, 'The staff he wanted to hire would have gotten him fired.' There's nothing more important to a coach's success, except his own leadership skills. When I would do interviews, a lot of times I would say, 'Give me [the names of] your staff, and then we'll take a break and decide whether this [interview] will continue."

Consider the plight of the Minnesota Vikings, who are on their fourth offensive coordinator of coach Mike Zimmer's five-year tenure. In January, Zimmer settled on John DeFilippo to replace Pat Shurmur, who left to become the New York Giants' head coach. As with McCoy in Arizona, DeFilippo's arrival generated public excitement, even as some around the league wondered if he was a good match for Zimmer's old-school approach. Zimmer fired DeFilippo 14 weeks into the season in what he called an attempt to "salvage" a 6-6-1 campaign. It remains to be seen if the Vikings can clinch a playoff berth and, if they do, whether their disjointed offense can function well enough in the postseason.

Speaking generally, Banner said, "There are a lot of people that are either misperceived or have been in the league long enough that maybe an accurate perception at one point maybe no longer is valid."

So how can head coaches ensure that their staffs will power them to a division title or into unexpected postseason contention, as we've seen in Chicago and Indianapolis, rather than sink a season? Both Banner and Casserly said one of the most common errors is friendship-based hiring.

"Coaches tend to hire people they know," Banner said, "and they feel like they can trust their loyalty because the level of fear there is about losing jobs in the NFL."

When he was the Browns' CEO, Banner instituted a policy that prevented managers on the business side of the building from hiring people they had worked with before. That approach probably isn't practical for coaching staffs, but its intent is worth considering.

Nagy, after all, had never worked with Fangio. He also had never been on the same staff as offensive coordinator Mark Helfrich, the former Oregon head coach. Lynn and Bradley hadn't worked together before joining forces in Los Angeles. And in Indianapolis, Reich had never even met Eberflus before he began the interview process.

The composition of a coaching staff can be a crapshoot. Timing is difficult to control. A strong candidate for one franchise could be a poor choice for another. But getting it right is crucial. It can be the difference between who is playing in January and who is already assembling a new coaching staff for the next season.