(EDITOR'S NOTE: This is an excellent, well-thought-out critique of the Packers' issues on defense. Thanks to MikeDB for putting it together.)
I do want to point out some problems with the Packer defense. The first major one is the difference between reality and expectations. The Packer faithful were expecting a major improvement to the defense from the last few years, mostly due to anticipation from defensive heavy drafting by TT during the past two drafts. It hasn't happened, and injuries to Jerel Worthy, Nick Perry, Casey Hayward and Clay Matthews have certainly contributed to the lack of significant improvement.
In addition, the Packer secondary has been too highly evaluated. Morgan Burnett has not morphed into Nick Collins, Leroy Butler, or Darren Sharper this year. Jerron McMillian has played his way to the bench, and he may be fortunate to make the team next year. M.D. Jennings is a serviceable back-up, unfortunately he is a starting safety for the Packers. Davon House is not Richard Sherman, nor even close. Sam Shields (though the Packers best CB) is not Darrelle Revis. And Tramon Williams has not regained his form from prior to the shoulder injury. In other words, rather than a defensive backfield loaded with transcendent talent, the Packers have average-to-good defensive backs, several of whom would not find a starting spot on other NFL teams.
While lack of play-making talent certainly contributes to the defensive problems, I also believe that Dom Capers bears much responsibility for the poor defensive play. Let me begin by acknowledging that Capers is a defensive genius. The 3-4 style defense that Capers and Dick Lebeau developed is used widely in the NFL. And many of the better defenses use it. Capers is also very creative in his defenses. However, Capers' problems lie elsewhere.
There are basically two types of defensive coordinators. One type worries less about scheme and deception and simply calls for his defensive players to outperform their opponents, i.e. to kick butt and dominate. The second type is very concerned with Xs and Os, designing defenses and schemes that deceive the opponent. Most (and the best) DCs are a combination of the two types. Capers, it would seem, leans far too heavily toward the second type. He relies too much on schemes, deceptions and Xs and Os.
Before getting into specifics I'd also like to point out that Capers appears to be cautious by nature. This can be seen in his frequent preference for defensive players who are "assignment sure;" and this does not only a reference to A.J. Hawk. Capers frequently talks of avoiding the big play. I think the loss of Nick Collins has contributed even more to his cautiousness as there is no longer a future HOF talent to back up the defense and cover errors. This is also seen the tendency of Packer defensive backs to allow easy 7-10 yard catches.
This has lead to the rather 'infuriating' overuse of the 2-4-5 nickel, or even sometimes a 2-3-6 or 1-4-6 dime package. One of the advantages of these defensive packages is that there is a lot more speed and quickness on the field, and theoretically that should help to minimize big plays. The fact that the Packers gave up several big plays to the Eagles last Sunday, even with a 2-4-5 nickel package, only reinforces the sense of need for more DBs and thus more speed on the field. However, the basic principles of a 3-4 defense are abandoned upon using a 2-man defensive line as the base defense.
As most readers understand football as well as (or better than) me, I will only briefly describe the purpose behind a 3-4 defense. By adding another linebacker and subtracting a defensive lineman, the 3-4 looks to increase the athleticism along the defensive front. It changes the expectations for the defensive line, also. The defensive linemen are no longer expected to be major play-makers, but rather their job becomes occupiers of offensive linemen. A good 3-4 defensive lineman should be able to take on two offensive linemen and keep them from getting to the linebackers. Their job, by occupying the offensive linemen, is to free up the linebackers (especially the two ILBs) to pursue the play and make the plays.(Perhaps, players such as Justin Smith and J.J. Watt have unrealistically raised expectations for 3-4 defensive linemen; they should be seen as the exception rather than the expected.)
When the defensive coordinator decides to use 2 defensive linemen as the primary defense, then more pressure is put upon ILBs and DBs to take on blockers, shed blocks and then make tackles. There are a few ILBs in the NFL who are capable of taking on offensive linemen, shedding their blocks and making plays on a fairly consistent basis - none of them play for the Packers. It may look great when the DC draws up the defense with Xs and Os, but he is putting his players in a position to fail. The missed tackles that result are not simply a matter of "poor tackling," but a result of asking more from players than they are able to give, i.e. taking on offensive linemen, shedding these blocks and then making a tackle. And because the two OLBs are playing much more like traditional DEs in a 4-3 setup, but without any outside linebackers, then the defensive backs are being asked to set the edge and make tackles in the run game. Of course, this again looks good on the drawing board, and defensive backs should be active in run support - but there is a difference between a CB giving run support and relying upon the CB to be the primary run stopper on outside runs. (As an aside, I think that Capers puts too much on defensive backs, which sometimes leads to the breakdowns in coverage.)
Unfortunately, the Packers 2-4-5 nickel has not been particularly effective against the pass, either. In a passing situation the 2-4-5 becomes, more or less, a 4-2-5 with two ILBs and undersized DEs. The pass rush in the Packers' case has been normally a simple 4-man rush (like you would find with any typical 4-3 defense) with occasional blitzes by an ILB and/or DB. Another advantage of the 3-4 is that the offense is never certain who will be rushing the passer. There are, of course, 3 defensive linemen who will most likely pass rush, but the 4th pass rusher could be any of the LBs. Also, as against running plays, the three defensive linemen occupy offensive linemen and help open lanes for smaller, quicker LBs. It also possible to pass rush with both OLBs and have a 5-man rush (a minor blitz). In any case, having a 3-man line with several possibilities brings more confusion to the offensive line and bigger bodies to occupy them.
I think that the defensive line is a strength of our defense, and it would seem that playing to our strength would improve the defense. On medium distance downs, where pass/run options are fairly equal, I could see packages with Mike Daniels, Datone Jones, and Johnny Jolly or B.J. Raji on the defensive line. On first down, and run downs I could see Jolly, Raji, Ryan Pickett and incorporating C.J. Wilson into the rotation. It should also be possible to run some 3-3-5 nickel packages in which one ILB is removed for a defensive back. This package offers more strength against the run and better options for the pass rush. Throwing the 2-4-5 out the window isn't the answer, but it shouldn't be our base defense. It should more properly be used in a 3rd and long (i.e. 10 or more yards) situation.
I would put myself among those who believe that the time has come for Capers to go. He did a great job installing his defense for McCarthy and the Packers. But now it is (probably past) time for one of his disciples to take over and improve upon what Capers has brought.