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Shell Coverages, Disguises, and Deceptions
How this year’s defense will build on how well they can mess with QBs and the box counts.
Bob SturmAug 19, 2026
We have time to talk a little more defense today and given how popular our last piece was about the nuts and bolts of what Vic Fangio and Christian Parker want to make a key part of the structure and design of their defenses, I thought we should cover a few items today that are very much tied together.
Now, to some of you, this is going to be very basic defensive structure and discussion, but remember, we don’t want to leave anyone behind here. I am sure CP himself would chuckle at how basic some of this information is, but trying to talk football tactics in a way where almost anyone can follow along is sort of my brand here. If you want to know the game in a somewhat deeper way, we want to have those discussions here. But, in doing so, the more advanced football fans and coaches who read this might suggest they already knew a lot of this. If so, please feel free to add thoughts in the comments to help everyone process the info. This has always been a community of football learning and I want to keep it that way – even for me.
With that in mind, let’s dive into our topics today - which were mostly in the headline of this very essay:
Shell Coverages, Disguises, and Deceptions
We must start here.What is a shell coverage?
Shell coverage refers to the deep secondary structure and initial alignment of the safeties in a defensive pass coverage. It describes how the defense organizes the deep part of the field before the snap and determines the basic family of coverage being played.Shell coverage almost always refers to two-high safeties and when it does, we will almost always call that “Middle Field Open” or MFO. In the diagram below, please spy the two safeties in pink:
The MFO family of coverages split the field in half and try to balance up the defense on either side. As you can see, you will usually have one more defender to the tight end side, but otherwise, everything is generally balanced.
The MFO coverages are usually the even numbered ones: Cover two, Cover four (quarters), and Cover six (which sort of splits the field with one half of it in cover two and the other half in quarters). These are all zone coverages, of course. Also, 2-Man is played from shell coverage which simply means two-high with man under.
What is single-high coverage?
Now, of course, if it isn’t two-high, you will almost always see single-high, which is also “middle field closed” or MFC.This is pretty easy to define, but here is the other diagram:
Now, if you want single-high, the other safety drops down to stop the run and to add that “8th man” in the box to load things up.
MFC coverages require that single high safety to cover a ton of ground and usually teams are vulnerable outside the numbers. To really simplify things, we should tell you that MFC almost always means Cover 1 or Cover 3. There are dozens of variations to each one (if you have played Madden, you are nodding) but Cover 1 is Man Coverage with a single high safety and Cover 3 is a zone coverage with the thirds of the field going to the two corners and the high safety (usually).
Still good? At the start of every play, I always look at the safeties. Why? I guess I want to know what the QB is thinking. But, to do that, I need to know score, down and distance, field position, and also personnel groupings. These are all variables that each side of the ball will use to compute the likely ideas of the other side.
But, it all starts with where are the safeties and what are they getting ready to do.
Why disguise has become a huge part of defense.
Ok, let’s say you are a defensive coordinator. What are the very first two things we want from our defense every day, every game, every season?- We want to all coordinated together and be on the same page in doing our job as an 11-man unit to stop our opponents in our best ways possible. We must not beat ourselves by not playing in concert.
- We don’t want the opponent to know what we are doing so that they cannot attack our weak spots so easily.
But, during 2025 the Cowboys did neither. The number of times that they were all NOT on the same page is too many to count. They were not playing in concert and the pieces were not talented enough to deal with much of anything. It might have been the worst Cowboys defense in years and the reason to explain that is too extreme to suggest is any other thing.
They beat themselves. They were understaffed. They were leveraged too heavily on guys who were not good enough. They were just mismatched.
Then, if you can believe this, they were so bad at so many things that they felt they could not even use disguise. They played a vanilla defense and played it without any deception or disguise. They basically were simple to figure out and had no talent to assist in the fight.
We can debate whether this was primarily the fault of the front office – who trades their best defensive player one week before the season starts and gets no immediate help back – or the coaching staff – Matt Eberflus seemed to do a horrendous job in so many aspects. But the truth is the defense was so historically bad, it doesn’t matter.
This 2025 Cowboys defense:
- Finished #32 (dead last) in scoring defense allowed (29.9 PPG) in 2025
- Ranked #32 in explosive play rate allowed
- #31 in pass defense efficiency
- #30 in run defense efficiency
So, the Cowboys would play a lot of MFC, but also a lot of MFO. They were right at about league average with both of those.
The big difference is that if the Cowboys were in MFC, they stayed in it. If they were in MFO, they stayed in it. They tried to deceive the opponents only 13.2% of the time in all of 2025 and that was dead last. 32nd! Now, there are some really good defenses that never disguise what they are doing, but I bet they had much more talent than Dallas to be able to do that. There are also awful defenses that disguise all the time, but they end up beating themselves.
How do we define disguise or late rotation?
Disguise is defined as pre-snap to post-snap. Teams now have late rotation to show a QB one thing as he looks you over and perhaps even changes plays. But, you are not really in that defense, you are just trying to mess him up. Your late rotation is what you are actually doing.So, we will basically show two-high and then play single-high, but by the time we reveal that, you are already in the play and it is too late to audible again.
Let me show you an example.
Dallas vs Philadelphia last November had plenty of this. The Eagles (with Fangio and Parker) were constantly trying to fool the Cowboys. The Eagles wanted the Cowboys to run into what looks like good numbers, but then rotate down and take away that advantage - especially on 1st down.
So, on this play, watch the safeties.
It starts two-high, but it isn’t. The Eagles are chasing the Cowboys off the pass, but then defending the run really well. The Cowboys got five yards, but the concept remains the same. The late DBs running downhill are what you want to see.
I went back through the tape to find why Dallas didn’t disguise more and I found that in Weeks 1-3, they only really tried to show MFO and then rotate to MFC and play man coverage. Well, the one time they tried it, Chicago killed them.
The Bears get a massive play as the rotating safeties were confused and nobody had the RB (yes, I think this was another Kenneth Murray bust), but the Cowboys kept simplifying things for their defense and in doing so made it too easy to attack.
When you are 32nd in points against and explosive plays against, you tend to simplify. But, this league is too good to play vanilla defense with no talent advantage.
Box Counts Mean Everything
The QB and OC always want to see that 2nd safety. Where is he? It will probably determine which play we run. “If it is even, we are leavin,” means eight men in the box is a deep pass.Remember - box counts still determine so much on base downs for offenses. It is why RPO’s even exist. Offenses always want to know the box counts. If you sit in two-high, you are daring the offense to run the ball. They will. And that is the battle.
The offense sees you don’t have enough troops so they will bleed you by taking 5-6 yards per carry. And yes, there is a ton of data that shows yards per carry are absolutely determined by box counts. A ton. A light box is 6 yards a carry. And it probably drops a yards per carry for every extra defender you put in there.
Meanwhile, defenses want to suppress big plays and they believe if you take 5 yards a carry, eventually you will have a penalty or a fumble and they will take their chances on 12-play drives, but they cannot let you flip the field with one big pass.
Fangio and Christian Parker’s disguise vs Dak - Nov 2025
I think it is reasonable to say that the Eagles vs Dak was the inspiration at looking at hiring Parker away. This cat and mouse game from November was fantastic, so let’s look at the two-shell disguise vs the Cowboys offense in that home game.Just to show you this “late rotation” disguise game, I went through and found like eight more examples of showing MFO and then rotating to MFC.
9:16 - 2Q
The late safety diving down to stop the run (32) is key. The Eagles know if they can get Blankenship down there, he is that extra hammer. But, George Pickens is trying to “dig out the safety” because that is how this works. You send a rotational safety, we need a WR to get to him before he blows it up. Here, Pickens pulls out so he doesn’t commit a penalty, but the Eagles beat him here. It didn’t matter, but that is why the creeping safety is trying to get a head start - because he knows the WR is trying to get to him before he gets to the ball.
9:16 - 3Q
Cowboys in 21 personnel and the Eagles show 2-high, but here comes 24 creeping down. This time, he is blocked by Flournoy (19) and it works out very well for Dallas in the run from their own end zone.
8:01 - 3Q
Here is a nice Malik Davis run into a late rotational safety. Watch the Cowboys WR get to Blankenship (32) and come close to a penalty, but Davis darts through in an instant. Isn’t it wild how fast it is all happening?
7:27 - 3Q
Same drive, here we go again. Once you see these plays, you see the battle between the WRs and the safeties in terms of blocking downfield. This then turns 33-DeJean loose and he gets to the ball and Malik Davis. DeJean is the big nickel and is who Caleb Downs will be trying to replicate.
3:02 - 3Q
Now, the downhill safety sometimes is blitz support and on 3rd and 5, if Dak sees pressure, then he knows that CeeDee Lamb is available in man coverage. It is one thing to spot it, but definitely another to put the ball right on Lamb’s hands from that far away. Dak played some exceptional QB in that he can kill defenses by seeing an opportunity.
13:09 - 4Q
Here it is again. Rotational safety switches to MFC after presnap is MFO. You are trying to play man with DeJean against George Pickens? No. Dak is going to attack, so you might stay in your zones next time. Disguise doesn’t insure anything against a veteran QB.
A couple more 4th Quarter runs into a late rotation run defender.
7:28 - 4Q
And the last one I found:
7:12 - 4Q
So what is the big takeaway here?
Well, Dallas is betting – like Philadelphia has bet – that they can stop your run with just six because their DT’s are so good. Jordan Davis and Jalen Carter there, Quinnen Williams and Kenny Clark here.
They also believe the 7th guy in the box is a DB who is a bit of a corner/safety hybrid in Caleb Downs/Cooper DeJean. Then, the two high safeties – Malik Hooker and Jalen Thompson – will show MFO and go to MFC. Or MFC and switch to MFO. They want to be coordinated, organized, and in concert. That is all the communication talk. On the same page and helping eachother.
And most of it will start in MFO because late rotation towards the box is more attack-mode than late rotation back to two-high because then your guy is running backwards.
It is a numbers game where you don’t want the offense sure of what your plan is until the play is happening. It will still lose at times because offenses are good and veteran QBs have answers for everything. But, it should increase your ability to function and to fight back a bit.
Something the 2025 defense hardly ever did.
