In my last post we saw some of the ways that our new 3-4 defense differs from the 4-3 that we've been running for the last four years. Even though the front is where the most obvious differences between the 3-4 and the 4-3 are, our defensive switch also has strong implications for coverage. In this post I'm going to describe our base coverage package, with an emphasis on how front play and pass coverage interact. By looking at how the various parts of the defense fit together, we can get an idea for the new strengths (and weaknesses) that our switch to the 3-4 will bring about.
Pass Rush by the Numbers
The most common coverages in football assume a four-man pass rush with seven coverage defenders on the back end. Cover-2, for example, is a 2-deep, 5-under zone coverage, Cover-3 is a 3-deep, 4-under zone coverage, and so on. This ratio of 4 rushers to 7 pass defenders is the norm.
When you run a 4-3 defense, your four rushers will almost always be the four defensive linemen. You can add unpredictability by bringing extra rushers on a blitz, but when you're only rushing four, it's obvious that those four will almost always be the DL.
One of the nice things about the 3-4, in contrast, is that a four-man pass rush will necessarily involve a blitz; you only have three defensive linemen on the field, and so if you bring a fourth rusher, it'll have to be a LB or DB. By mixing up who that fourth rusher is, you can add unpredictability to what would otherwise be a vanilla 4-man pass rush.
Playing Cover-4 in the 4-3
Under both Buh and Kaufman, our primary coverage was Cover-4 (a.k.a. Quarters). This is a zone coverage, and works by putting three defenders (CB, Safety, and OLB) in a triangle over two receivers:
To oversimplify the coverage, the CB lines up outside of everybody and takes the first receiver who comes outside. The OLB lines up inside everybody and takes the first receiver who comes inside. The Safety lines up deep and takes the first receiver who runs deep. All three defenders are in a great position to carry out their assignments.
That all sounds good, but Cover-4, like all coverages, has some weak spots. One problem, for example, is that it can be weak in the flats:
Remember that this coverage wants to use the CB to defend outside-breaking routes. When the inside receiver (H) runs an out route, then the CB should be there to take it away. In the diagram, however, we see that the outside WR (X) is running deep. This can influence the CB to run deep as well, which vacates the flat and takes that CB out of position to defend the out route to H. Furthermore, because the SLB is lined up inside, he’s going to have a tough time defending this play.
This is the kind of thing that Cover-4 can be susceptible to. If you want to eliminate this weakness, then you have to change your players’ alignments. Here’s a variant called 4-Robber, which we also ran a lot with Kaufman:
The key here is that the SLB has shifted to an alignment outside of the H receiver. This change in alignment puts him in a good position to defend out-breaking routes, and relieves the CB of the burden of covering these routes. This frees up the CB to play tighter, more aggressive coverage on the X receiver.
DeRuyter’s Answer in the 3-4
In the spring game, our default was to widen the OLB’s (Sam/SL and Jack/JL) much like we saw in 4-Robber. Our OLB’s were basically playing heads-up over the slot receivers:
When those slot receivers ran outside, the OLB’s ran with them, giving us good, aggressive coverage in the flats and freeing up the CB’s to play aggressive coverage on the outside:
Because those OLB’s are out wide in coverage, our fourth pass rusher (if we use one) will be an ILB (either Mike/ML or Will/WL):
OK, so we can get our 4-man rush, and we’ve found a way to defend the flats. That’s nice, but it also opens us up to some new problems. Now, because those OLB’s have widened, they’re more vulnerable to getting beat to the inside:
This is a new problem that we’ve created by pulling our OLB’s to the outside, and we need an adjustment to make sure that we don’t get killed by it.
Changing up the Blitzer
Above, when we talked about switching between plain Cover-4 and 4-Robber, I mentioned that changing your coverage requires a change in alignment. This alignment change, unfortunately, makes it easy for the QB to tell when you’ve made an adjustment. If your SLB is lined up to the inside, then you’re in plain Cover-4:
If your SLB is lined up to the outside, then you’re in 4-Robber:
The SLB has to line up in different places to be able to carry out his different assignments, and so his alignment gives the QB a useful key.
In DeRuyter’s 3-4, on the other hand, we don’t have to change anyone’s alignment to make coverage adjustments. Instead of changing our LB’s alignment, we can just change up who the blitzer is. If we want to play wide and take away the flat, then we can blitz an ILB and leave the OLB’s in coverage:
If, on the other hand, we need to take away the inside, then we can keep the exact same pre-snap alignment, but blitz a different LB:
In this last diagram, the slot receiver (Y) runs a slant, and the Will (WL) is sitting inside in perfect position to defend it. We’ve changed our coverage by changing the blitzer, but we’ve done it without changing anybody’s alignment and tipping off the QB that something new is coming. In this way, by playing a 3-4 and having flexibility in terms of who our fourth pass rusher will be, we can keep our coverage adjustments hidden until after the snap. The 3-4 gives us this kind of versatility, and fits well with DeRuyter’s desire to constantly mess with the QB’s reads.