San Francisco 49ers: What Will Happen to the Defense with Vic Fangio's Departure

The San Francisco 49ers won’t have to face ex-head coach Jim Harbaugh anytime soon, as he’s gone off to the University of Michigan.  Nor will they risk being bitten by former offensive coordinator Greg Roman, as they won’t play the Buffalo Bills until 2016.  However, it looks like at least one old coach will get a shot at revenge at the franchise.

As first reported by NFL Network's Ian Rapoport and confirmed by the Bears via Around the NFL's Marc Sessler, Vic Fangio will be headed to the Chicago Bears to serve as their defensive coordinator under new head coach John Fox.  That’s a fantastic hiring for the Bears, getting one of the most highly sought-after coordinators to revitalize a defense that was 30^th in yards allowed and 31^st in points allowed.

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We don’t know yet who will replace Fangio as the 49ers’ defensive coordinator.  Earlier in the week, all signs pointed to it being former Oakland Raiders coordinator Jason Tarver.  Tarver’s defense was actually the only team in the league that allowed more points than the defense Fangio is taking over, which would have ended up being an odd coincidence.

However, NBC Sports' Josh Alper noted Wednesday, via multiple reports, that Tarver’s role on Jim Tomsula’s staff will be as linebackers coach, not defensive coordinator.  Another rumor has Eric Mangini as defensive coordinator, with Rapoport reporting via Twitter that Mangini is speaking with the 49ers.  Mangini served as tight ends coach for the 49ers last season and was a senior offensive correspondent for the team the year before.

Until a hiring is made, the 49ers remain the only club without either an offensive coordinator or a defensive coordinator in place.

So, in 2015, you’ll have the coordinator from one of the best defenses in football taking over one of the worst, and an entirely unknown quantity taking over one of the best.  What effects will that have on both franchises?  It would be an interesting litmus test—how much impact can a coordinator have on a team?

This is not a prediction, or even a suggestion, that the Bears defense will be better than the 49ers defense in 2015.  The talent gulf between the two franchises is still enormous, and even if Fangio were the absolute perfect coordinator and whoever the 49ers hire were the absolute worst coordinator, there isn’t a formation or scheme that can hide that big of a talent gap.

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For the Bears, there’s nowhere to go but up.  Fangio should be able to step in, reshuffle the existing parts around, bring in some free agents and see an immediate jump in quality. 

Ego Ferguson has the size of Quinton Dial, so he’ll be able to move to the 3-4 nose tackle position, the non-Lance Briggs linebackers should fit into Fangio’s scheme perfectly, and defensive backs coach Ed Donatell should be able to coach up Brock Vereen and Kyle Fuller.  I don’t expect them to be league average next season, but they should get significantly out of the basement.

Then again, sheer regression to the mean would see that happen some.  It’s hard to be as bad as the Bears were multiple seasons in a row.  They were in the bottom three in both yards and points the last two seasons; the last team ranked that low for three consecutive years was the 2007-09 Detroit Lions.  The simple law of averages would indicate the Bears would be somewhat better in 2015.

That brings us back to the 49ers, and the actual point I’m making here.  The 49ers have one indicator that the defense should be significantly worse in 2015, and one indicator that it should be even better.  The indicator that it will be worse is that simple law of averages.

The 49ers have finished in the top five in yards allowed for the past four seasons—every year Vic Fangio was in charge of the defense.  They hadn’t ranked that high since 1997, and hadn’t done it for four straight years since the 1987-90 seasons, a run which produced two Super Bowl victories.

It is mind-bogglingly difficult to keep that level of success up without changing coordinators and schemes.  The last team to do it was the 2007-12 Pittsburgh Steelers, with a defense led by Hall of Famer Dick LeBeau.  The Steel Curtain ‘70s Steelers couldn’t do it.  The early ‘00s, Ray Lewis-led Ravens couldn’t do it.  The Warren Sapp-led Buccaneers couldn’t do it.

Why is it so hard to stay at the top?  For one, success breeds copycats.  Even if Fangio had had the opportunity to stay with the 49ers this season, he probably would have still lost top assistants like Ed Donatell, who had interviews for defensive coordinator positions. 

Talent leaves, too—last season, the 49ers had to let Donte Whitner and Tarell Brown leave thanks to financial limitations.  They managed to replace both players last year, but to keep succeeding at a high level, you need a constant stream of top-level players, and that’s a hard task to accomplish year after year.

Players age, too—Patrick Willis is entering the backside of his Hall of Fame career and hopefully will age gracefully over the next four to six seasons.  Justin Smith is considering retirement, and neither Ahmad Brooks nor Antoine Bethea is precisely a spring chicken, both being well over 30 years old.

So, just from sheer regression to the mean, you’d expect the 49ers defense to eventually drop out of the top five—I mean, they’re not going to be a great defense from now until the end of the NFL.  A season when they’ve lost their coordinator would make a lot of sense to be that season, right?

Here’s the thing, however—the 49ers also have a great sign for the defense being better than it was in 2014, simply due the fact that injuries and suspensions also generally regress to the mean.

Football Outsiders has a statistic called Adjusted Games Lost, where statisticians take a team’s injuries and adjusts them based on importance to the roster, so injuries to a player like NaVorro Bowman matter more than ones to a player like Kassim Osgood. 

They’ve yet to produce their 2014 numbers, as the season isn’t over yet, but what’s important is that they’ve found there is little to no correlation from year to year—that is, a team with a ton of injuries one year isn’t any more likely than any other team to have a ton of injuries the next season.

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The 49ers, of course, were racked with injuries on defense in 2014.  They ended the season with Patrick Willis, Jimmie Ward, Ian Williams, Chris Cook, NaVorro Bowman, Glenn Dorsey and Chris Borland all on injured reserve.  They also lost significant time from Aldon Smith and Tramaine Brock.  Whoever the 49ers' next defensive coordinator is will almost certainly have a more complete roster to work with.

Those injuries, of course, are what made Fangio’s performance in 2014 so incredible.  It’s one thing to produce a top-five defense with a roster full of Pro Bowlers; it’s quite another when you’re dipping into the likes of Nick Moody as a sixth-string linebacker starting for you at the end of the season. 

If we could guarantee that the 49ers would have the same number of injuries in 2015 as they did in 2014, I think there’s no doubt that they’d fall back to the pack.  There are few, if any, coordinators in football who could have pulled together that injury-hobbled unit and produced a gem.

But, in all likelihood, the 49ers will get a healthier team back in 2015, and that’s why it’s so difficult to figure out how good the defense will actually be.

My hunch—and, until there’s an actual defensive coordinator with a strategy and scheme in place, it can only be a hunch—is that the effects of age and entropy will harm the 49ers more than returning players will help them.  Asking for a fifth straight year of top-five defensive play, considering all the turnover on the staff, is probably too much to ask for. 

Players will be asked to fill unfamiliar roles in the front seven, have a new set of terms and codes to learn and generally be asked to do things differently than they have the last four years.  There are bound to be some growing pains.

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However, the defense is too talented for them to fall all the way back to the pack.  A healthy NaVorro Bowman will be a huge boost, as will the return of Tramaine Brock.  It will be exciting to see Bowman working alongside not only Patrick Willis but also Chris Borland in base defensive sets; that’s a unit most teams would be dying to have.

All in all, then, the 49ers defense should still be better than Vic Fangio’s defense in 2015; the raw talent gap is simply too large.  However, with Fangio’s expertise in the Windy City rather than the City by the Bay, I predict the Bears' defense will rise some and the 49ers’ will fall back to the pack some.  It’s the beginning of a new era in San Francisco.

Bryan Knowles is a featured columnist for Bleacher Report, covering the San Francisco 49ers.  Follow him @BryKno on Twitter.