So What Exactly Is a Mike Zimmer Defense?

You hear it often these days. "He'll fit well into a Mike Zimmer defense." Or, "Viking's defense poised for success under Zimmer," or "Zimmer's defense is transforming Vikings defense into a top unit." Or something similar. But what you don't hear so much about is exactly what is a Mike Zimmer defense? What makes it different or special? How does it work?

Let's have a look into how Mike Zimmer has managed to have so many top ranked defenses over the years, and his latest project, the Minnesota Vikings defense, which is quickly becoming another one.

Mike Zimmer's Track Record

Since Mike Zimmer first year as a Defensive Coordinator in 2000 with the Dallas Cowboys, here is his defensive track record in terms of league rankings in average yards per game allowed (YPG / A), average points per game allowed (PPG / A) and takeaways (TkA):

Year	Team	YPG / A	PPG / A	TkA
2000	Cowboys	19	22	20
2001	Cowboys	4	20	23
2002	Cowboys	18	13	11
2003	Cowboys	1	2	20
2004	Cowboys	16	27	25
2005	Cowboys	10	12	21
2006	Cowboys	13	20	8
2007	Falcons	29	29	17
2008	Bengals	12	19	17
2009	Bengals	4	6	19
2010	Bengals	15	24	17
2011	Bengals	7	9	22
2012	Bengals	6	8	8
2013	Bengals	3	5	3
2014	Vikings	14	11	25

Source: Pro Football Reference

Looking at Zimmer's track record, and considering that the Vikings defense ranked 31st and 32nd in yards and points allowed in 2013, what stands out is how quickly he was able to take a mediocre (or worse) ranked defense and mold it into a top ranking unit, with the exception of takeaways, which has often been average.

In Dallas, Cincinnati and Minnesota, team defense improved dramatically in the first years under Mike Zimmer. The only exception was Zimmer's one-year stint in Atlanta, which was aborted with Bobby Petrino's quick abandonment which drew the expletive-laced ire of Zimmer - and for good reason.

But overall, Zimmer has quickly put together top defenses wherever he has gone. Interestingly, the worst stretch of rankings Zimmer had after establishing a top defensive unit came in Dallas after Bill Parcells took over as head coach, and had him implement a 3-4 system, which he had not used before- or since.

Another interesting measure of the quick improvement under Mike Zimmer comes from PFF stats. In 2008, Zimmer's first year with the Bengals, the defense had an overall rating of -107.1, with nearly all of the negative numbers coming from an abysmal defensive line, with player turnover, particularly against the run.

In 2009, Zimmer's defense improved to -45.8 overall, an over 60 point improvement, largely due to big improvements in run defense up front, and pass coverage by CBs, particularly Jonathon Joseph and Leon Hall. 2010 continued the improvement, this time to -18.3 overall, primarily by a big improvement in the pass rush with the addition of Geno Atkins, and better run defense with continued improvement up front, and the addition of Ray Maualuga.

But it wasn't until 2011 that Zimmer's overall defense turned positive (+11.1 overall), largely due to the pass rush of Atkins and Carlos Dunlap. This despite turnover in the secondary, and a weak defensive line outside of Atkins and Dunlap.

2012 was the year of Geno Atkins in Cincinnati, who accounted for +73.6 points of the +84.9 overall rating for the Bengals defense- another huge improvement overall.

In 2013, Atkins fell back to earth a little, still +17 overall, but Michael Johnson, Vontaze Burfict and James Harrison all did well en route to a +43.3 overall PFF rating.

It is interesting that it took Zimmer a number of years to bring in some better players on defense, and throughout his tenure in Cincinnati there was a fair amount of turnover in the secondary, and at linebacker, and never solid play across the entirety of the defensive line. It's also interesting the Robert Geathers, LDE for the Bengals, started all six years Zimmer was there, but was always at least double digit negative in his overall PFF rating, including back-to-back years of over -20 overall ratings.

But from a PFF statistical standpoint, Zimmer's greatest one year improvement came last year with the Minnesota Vikings. In 2013, the Viking defense had a -70.3 overall rating, including a -50.2 rating in pass coverage, and a -30.1 rating in run defense. Last year, the Vikings improved dramatically to a +54 overall, including a +37.6 in run defense, and a +8.1 rating in pass coverage. That represents a +124 point swing in one year- largely with the same roster.

How did he do it? How did he make such an impact in only one year? Let's have a look at what could be the reason(s).

Characteristics of a Mike Zimmer Defense

One characteristic of often mentioned of Zimmer's defenses is that they tend to be "no name" defenses- lacking a lot of star power. That is certainly true. Geno Atkins is perhaps the biggest star from Zimmer's tenure with the Bengals, and he didn't arrive on the scene until it was half over. Leon Hall and Chris Crocker had a number of good years under Zimmer at CB, but hardly household names- either one. James Harrison wasn't there long either, and guys like Burfict, who's had up and down years, are more known as troubled players Zimmer was able to turnaround.

Beyond personnel, Zimmer's defenses are often characterized as aggressive, designed to put pressure on the quarterback. Perhaps a signature of a Mike Zimmer defense is the 'double A gap' blitz formation, with two linebackers on either side of the center, showing blitz. But beyond these general characteristics, what are the nuts and bolts of Zimmer's defense- how does he get such good results?

Key Scheme Elements of Zimmer's Defense

• 4-3 base scheme, frequent use of 4-2-5 nickel package in passing situations
  
• primarily press-man coverage
• extensive blitz variations, including signature double-A gap blitz formation, but does not blitz frequently
• Stop the run first mentality

Looking at these elements, most of them are not particularly unusual, and most are commonly used in NFL defenses. And yet, as Robert Klemko at SI.com pointed out a couple years ago:

"Zimmer’s defense isn’t your grandmother’s 4-3. It’s constantly evolving based on the personnel, and constantly trying to amp up pressure by creating mismatches with an array of stunts and bluffs...

They might load eight in the box, appearing to bring a heavy blitz, only to throw the quarterback a curveball by rushing the corner from the slot side and rotating a safety from his pre-snap blitz position to fill the vacancy. They might fake an inside blitz, leaving interior blockers searching for someone to hit while the quarterback gets rolled up by edge rushers"

Bill Belichick, head coach of the Patriots, summed up Zimmer's defensive looks pretty well when the Vikings played them week two, after having been totally shut-down the previous year against Zimmer in Cincinnati:

"They disguise well; including the linebackers, whether that’s (Anthony) Barr and (Chad) Greenway or when they put Barr down, Greenway and [Gerald] Hodges and all those guys do a good job of blitzing and covering and faking and man, zone," Belichick said. "That’s really the scheme that Coach Zimmer runs. They do a good job with it. They’re all part of it."

Belichick continued: "I’d say that’s one of their real strengths is they give you a bunch of, not so much different looks but different combinations off similar looks. You have to be ready for everybody…Sometimes it’s strong side, sometimes it’s weak side, sometimes it’s up the middle, sometimes it’s man, sometimes it’s zone, sometimes it’s blitz zone, sometimes it’s all-out blitz, sometimes it’s just max coverage and they drop everybody off but off that same look."

Most, but certainly not all, of these variations come off of the double-A gap blitz formation. Needless to say, Belichick and company, despite having problems at offensive line, did a much better job against the Vikings defensive than they did against the Bengal defense the previous year. A good deal of the reason, besides the difference in personnel, is perhaps more experience and better preparation.

The double-A gap blitz is gaining popularity in the copy-cat NFL- much to Zimmer's chagrin- but even if it isn't an exclusive element in Zimmer's scheme, he is one of the more accomplished and advanced practitioners of it. In any case, more teams have adopted it, and more teams are planning against it- not just in weekly preparations but in the off-season as well.

But, if you are looking primarily at the key scheme elements of a Mike Zimmer defense, the double A gap blitz formation is one to explore, as it has brought continued success over the years.

The Double A Gap Blitz Package

At the beginning of last season, there was some discussion about Mike Zimmer's defense, and it's signature element in Cincinnati- the double A gap blitz package. It is a variation of a nickel or 4-2-5 package typically, with linebackers in both A gaps on either side of the center. Arif Hasan did a great analysis of it in action, and in an interview with the StarTribune, Matt Birk gave a good explanation of how difficult it was to stop when he was with the Ravens, and some of the advanced ways Zimmer implements the package.

The bottom line with Zimmer's signature blitz package is that by menacing both linebackers in the A gaps on 3rd and long situations- when it is often used- it creates the urgent need for offenses to make adjustments. Adjustments to blocking assignments, play adjustments, receiver adjustments can all be involved. The difficulty is that if all the adjustments are not made properly, the play fails. Either a defender is given a free path to the QB in the event blocking assignments are not adjusted correctly, or a pass is not completed if a QB or receiver fails to make a necessary read/route adjustment.

The reason for the adjustments and the difficulty in stopping this blitz package is because it often relies on deception. The linebackers don't always blitz. Sometimes one or both drop into coverage, other times they do blitz and a DE drops into coverage- otherwise known as a zone blitz. And still other times one linebacker may blitz, and a DE drop into zone coverage and a safety or CB blitzes too. Who does what on a given play can also be determined by certain keys or triggers to create match-up advantages. The intent is to create confusion, or even a momentary hesitation, in blocking assignments so a free rusher gets to the QB or forces an early in-completion.

The aggressive and deceptive nature of the blitz package force an offense to raise their level of execution. Undoubtedly every offense practices how to execute against this package the week they play the Vikings, and our NFC North opponents plan for it in the off-season as well. This in turn creates a need to add new dimensions and difficulty to the package, which Zimmer is perhaps the most advanced in creating. Adding keys and triggers for who blitzes when can make this package even more difficult to block and even more successful in getting the defense off the field.

For example, very early in the home game against the Packers, the Vikings showed a double-A gap formation on first and 10. Most likely this was a bit of a surprise- early and on that down and distance (perhaps thrown in early to see how they react for future reference) and there was a lot of chatter among all the Packer players after they got up to the line. Rodgers had either called or audibled a pass, and the LBs went back into coverage rather than blitzing, coverage was good and it resulted in a broken play (although Rodgers did manage to run for a decent gain). Later in the game, however, with Rodgers in shotgun, the Vikings showed the double-A gap blitz formation and the Packers motioned the TE to just off-center - in an interesting counter to the formation to either block the blitzing LBs, or, presumably, go on a route if they drop into coverage, perhaps creating a tough route for the dropping LB to cover.

Bottomline, despite the addition of the double A gap blitz formation, which is used primarily on 3rd down situations, the Viking's opponent 3rd down efficiency declined only slightly from 44.2% (30th in league) in 2013 to 41.5% (20th) in 2014. Zimmer's defenses in Cincinnati went from 38.6% in 2009 to 32.9% (2nd in league) in 2013.

Perhaps the reason for the limited success was due to the Vikings defensive personnel not being as experienced and adept in using the package, and perhaps it is also due to more preparation by opposing offenses. Time will tell.

Press-Man Coverage

In today's passing league, and with the prevalence of west coast offense principals, press-man coverage seems much better suited for success than the Tampa-2 zone coverage the Vikings employed for years prior to Zimmer. It's not that zone coverages are not used under Zimmer (they are), or that they are ineffective. But disguising coverages and being able to play either effectively on a given play is important, and that was not the case so much in previous years. It was often very frustrating to watch a quarterback skilled at exposing the weaknesses of the zone defense, such as Aaron Rodgers, complete seam routes effortlessly it seemed at one point, and at another take advantage of a big CB cushion to complete an easy out route for a first down.

And yet, comparing the opponent target completion percentage, or what percent of passing targets (not including throw-aways) were caught, from 2013 to 2014, with the switch from Tampa-2 to more press-man coverage, it went from 66.7% in 2013 (27th in the league) to .... 66.9% in 2014 - still 27th in the league.

Hmmm. The Vikings improved over 58 PFF rating points in pass coverage last year, but didn't gain any ground whatsoever in overall opponent target completion percentage.

One pass defense statistic that was OK in 2013 but improved in 2014 was opponent receiving yards per attempt (total passing yards allowed/receptions). In 2013, that number stood at 11.6, or 14th in the league. Last year the Vikings defense shaved nearly a yard off that average, or 10.7 yards, good for 5th best in the league.

The big jump in pass defense came in average passing yards per game allowed. In 2013, that number was 287.2 yards, or 30th in the league. In 2014, that number declined significantly to 236.8, or about 50 yards a game, good for 8th in the league.  That number was aided both by the average receiving yards per attempt stat above, and also by having fewer passing attempts against.

Another significant improvement in pass defense came in the category of receiving TDs allowed. In 2013, the Vikings defense was dead last in the league, having given up 37- four more than the next worst. But in 2014, that number dropped to a more respectable 26- tied for 18th in the league/

Run Defense

Like most defensive coaches, Mike Zimmer focuses on stopping the run first. The idea being that by stopping the run, you force your opponent to become more one-dimensional, more predictable, and create more favorable opportunities to get your defense off the field.

But, in Zimmer's first year with the Vikings, average rushing yards per game actually increased, from 110.4 yards per game in 2013 (16th in the league), to 121.4 or 25th in the league. Similarly, rush yards per attempt allowed increased from 4.0 to 4.3 yards in 2014, which was 23rd in the league.

Overall Defense

Overall, the Vikings defense improved in several key metrics since Zimmer took over- other than average yards and points per game allowed- and overall PFF rating. Average yards per play allowed decreased from 5.62 (24th in the league) to 5.38 (14th), opponent scoring efficiency (drives that resulted in points) decreased from 39.6% (29th in the league) to 34.1% (17th). Also, red zone defense improved, allowing TDs only 54.17% of the time when the opponent reaches the red zone, vs. 61.9% in 2013.

But can we chalk this up to Zimmer's scheme elements? Perhaps a little. But I suggest another reason.

What Really Made The Difference

The big jump in defensive performance last year is not so much about Zimmer's scheme, as it is about Zimmer's coaching. Zimmer has said he wants good teachers as coaches. And Zimmer himself has often been agnostic when it comes to scheme, preferring to focus on adapting his scheme to fit his players:

Honestly, I want to fit our scheme to the players to the best of their abilities. Like I said before, it really does not matter if it is a three-four or a four-three, and as far as my philosophy I want to stop the run and I want to hit the quarterback. However that is, if we got to blitz I think we have a great blitz package, but I want to be fundamentally sound in what we do. There are teams that can go out there who can go out and make a lot of big plays, but they are not fundamentally sound. Then when the game gets on the line, they do not perform in the crucial situations of the game.

In Zimmer's first year, it's been more about coaching than adapting scheme to his players. Most of what Zimmer did scheme-wise last year was carry-over from Cincinnati. Getting used to his new situation, new players, etc. didn't allow for much time to begin to adapt scheme much to his current personnel, particularly as injuries over the course of the year made that process more difficult and inopportune.

But I look at the jump in performance of not just players like Harrison Smith, Sharrif Floyd and Xavier Rhodes, but also later round picks like Josh Robinson and Robert Blanton. While these latter two players have not exactly been top performers in their position, Zimmer and his staff did fashion them into serviceable players. Blanton was the 2nd highest rated Vikings' DB last year overall by PFF, after Harrison Smith. Prior to Zimmer taking the helm, Blanton, a converted CB, had very little playing experience, and Robinson had basically been a bust.

Floyd and Rhodes, both first-round picks with high expectations, didn't really shine their rookie years, but did take significant leaps forward their second-year under Zimmer. Rhodes was helped in part by playing more press-man, which he prefers, while Floyd may have been helped in some instances by Zimmer's varied blitz schemes. Both proved to be much more consistent, which owes mainly to good (or better) coaching.

Zimmer, who got his start in the NFL as a defensive backs coach, has remained more hands-on as a head coach when it comes to coaching players- particularly at the DB positions. And so getting more consistent play out of Xavier Rhodes, while getting a guy like Josh Robinson to be an okay outside CB, where he had allowed something like a 97% targeted completion percentage when targeted in previous years- playing primarily slot CB- was a significant achievement.

Overall in terms of improvement in pass coverage, the lions share was among the DBs. Linebackers like Greenway and Brinkley, who aren't likely to improve much by coaching, remained the biggest holes in pass defense. This may also help to explain the lower yards-per-reception allowed number, and lower average passing yards allowed per game, while completion percentage being basically unchanged- QBs were forced to check down to a LB-covered receiver, as CB/S coverage improved.

Overall, most starters on defense improved and/or did reasonably well - including rookies and first-year starters last year. The notable exceptions were Chad Greenway and Brian Robison, primarily due to age (and injury), not coaching it is reasonable to assume, and to a much lesser degree Jasper Brinkley, Linval Joseph and Captain Munnerlyn- interestingly all free-agent acquisitions- although Brinkley was originally drafted by the Vikings. Munnerlyn admitted after the season he could have done a better job listening to Zimmer, which probably didn't help his cause, in more ways than one. Joseph said near the close of the year that, "it was hard to do what they asked me to do" when the season began, so that explains some of his regression- of course getting shot in the leg didn't help either- but he thinks things are coming together and this year will be a great year.

Work In Progress

So, while player performance improved generally, the product of good coaching, Zimmer's system was still new, and the Vikings are not there yet in terms of mastering it. A usual refrain from Zimmer in after-game press conferences was to lament that they could have done a lot of things better, often focusing on the defensive side. Moreover, Zimmer and his staff did not have ample time to really adapt his scheme to fit player strengths, and to play more cohesively as a unit. In part because it was still early in learning the system, and in part due to some injuries later in the year- both understandable. Still, a guy like Harrison Smith, who was already relatively sound fundamentally, versatile, instinctive and experienced, was in a good position for Zimmer to adapt his scheme to fit his abilities.

It is possible to imagine Zimmer adapting his scheme in the future to better fit Anthony Barr in particular, but also Everson Griffen and Sharrif Floyd, perhaps even Captain Munnerlyn, and later Eric Kendricks and Trae Waynes, as they are able to demonstrate their solid fundamentals, versatility, and experience.

But this will be the subject of another write-up, looking into how the progress, experience and new players on defense may drive changes this year, and down the road.