Two-Factor Blitz Theory

I received some pushback from yesterday’s Billy Davis rant, so today I’m going to try to add some nuance to my explanation.  First, I want to note that while Davis bears the brunt of my criticism, he’s certainly not the only DC I disagree with on a fairly consistent basis.  Graded against everyone else, Davis is OK (for now).  However, as is usually the case, just because everyone else does something doesn’t mean we need to do the same thing.  Conventional wisdom, especially in sports, frequently lags the “optimal” strategy.

So….Defensive Strategy, and more specifically, the Blitz.

My general take on this is that the Blitz (sending more than 4 pass rushers) should be viewed as a TOOL, not a general philosophy.  I realize that in Philadelphia, that’s borderline heresy (lot of Jim Johnson fans out there).  But let me explain.

Two Factors

To complete a pass, two things must happen (generally speaking): an “open” receiver must exist, and the QB has to identify that opening (after which he presumably throws the ball there).  It’s tough to determine what constitutes an “open receiver”, so I’m going to discuss this side of things in terms of Windows.  So a passing window refers to an opportunity to place the ball where the receiver can catch, and one must exist and be identified in order to complete a pass.  Simple enough?

Also, for a QB to identify the available passing window, he must have TIME to do so.  The more time he has, the higher the odds of him seeing an existing window or of one developing.

By breaking the process down into these factors, we can see the basic trade-off in defensive strategies (against the pass).  The best of both worlds, of course, is to minimize the passing windows AND minimize the time the QB has to identify them.  That’s why DEs are so coveted.  If you can generate a strong rush (i.e. lower QB time) with just 4 d-linemen, you can use everyone else to close passing windows.  However, very few teams area able to do that on a regular basis.

More often, you have to make a choice.  You can rush an extra man (blitz), which should decrease the amount of time the QB has to see a window.  Conversely, you can rush fewer men, and use more of them to minimize the windows.

With me so far?  Good, now let’s talk a little bit about passing windows.

Passing Windows

Passing windows open and close throughout each play.  A complete pass occurs when one of them opens and the QB hits it.  To help illustrate, I’ll pick a random frame from Sunday’s game:

Screen Shot 2013-12-31 at 9.57.59 AM

Nice….Now let’s superimpose the passing window on it.  Despite the outcome of the play (Boykin game-saving interception), there was, in fact, a window to hit here for Orton.

Screen Shot 2013-12-31 at 10.02.04 AM

That’s a rough approximation, obviously, but you can see the idea.  Given such a big opening, how the hell did Orton miss?  Any guesses?

How about:  He’s not a good QB!?

That’s a little unfair (just a little), because every QB misses opportunities sometimes.  However, let’s dig a little deeper into this.

When deciding what pass-rush strategy to use, there’s perhaps no greater factor for consideration than the skill of the opposing QB.   We now have to combine the QB skill with our Window illustration from above.  Let’s visualize it like this:

Screen Shot 2013-12-31 at 10.11.23 AM

Don’t get too caught up in the relative sizes, this is far from a “to-scale” illustration.  In the middle we have the passing window.  On either side I’ve provided a visual representation of each QB’s (Peyton and Orton) accuracy.  Think of the two layers as confidence intervals; something like 70% certainty the ball will end up within the smaller red circle and 90% certainty it will end up within the outer circle’s boundaries.

Hopefully this is rather intuitive.  Now play a mental game using those images.  The green square will move across the screen from left to right.  You control the red circle, and your job is to align it with the passing window and and press go.  Think of it like aiming a rifle.

Now…which player’s range (red circles) would you rather play with?

Easy, Peyton Manning’s, because his confidence ranges are smaller, meaning there’s a smaller margin of error.  For example, let’s say you align each perfectly with the passing window:

Screen Shot 2013-12-31 at 10.19.15 AM

See the problem?  The window is smaller than Kyle Orton’s accuracy range.  Meanwhile, it the window is significantly larger than Manning’s 70% accuracy range.  The upshot, naturally, is that Manning is a lot more likely to complete this pass.  Going back to our game image above, we can visualize the pass like this, with the yellow X denoting the final placement of the ball, which was intercepted.

Screen Shot 2013-12-31 at 10.23.35 AMMoreover, we can extrapolate the idea.  In general, Peyton Manning will be able to hit smaller windows than Kyle Orton will.  Obviously, smaller windows occur more frequently than larger windows, hence Peyton Manning, by virtue of his accuracy, will have many more opportunities to complete passes than Kyle Orton.

Now pretend you’re a defensive coordinator.  Remember you have a choice to make between eliminating passing windows and minimizing time.  In this exercise, you cannot do both.  Against which player is the “window elimination” strategy more likely to work?

Easy (again), Kyle Orton.

Since Peyton Manning’s required window size is so small, eliminating them will require extremely good coverage.  More likely, you can play excellent coverage on the receivers and STILL not prevent several of these small windows from opening up.

Conversely, against Kyle Orton, things aren’t so difficult.  He needs a relatively large window.  Large windows are easier to eliminate.  You don’t have to play perfect coverage. Notice in the Boykin play, there was a relatively large are in which Orton could have complete a pass for a big gain.  Fortunately for the Eagles, Orton didn’t hit his spot.  Boykin’s coverage was far from perfect, but it didn’t need to be!

In light of that, go back you your strategy decision.  Which do you think is easier to do:

- Eliminate windows

- Minimize time

Now consider that Orton was operating out of 3-step drops for much of the night.  Then, the answer is easy.  Eliminating his passing windows is the much higher-probability play.  Note that’s the BASE strategy.  Obviously, you need to blitz every once in a while, if for no other reason than to add some unpredictability.

That’s the crux of my argument against Billy Davis’ blitzes.  He doesn’t seem to vary his usage as much as I believe he should, and he doesn’t save his blitzes for high-leverage situations.  Instead, he uses them in LOW-leverage situations, where the reward of a sack is comparatively low, especially when weighed against the odds of a big play.

Against a great QB (like Drew Brees this week), you have to be much more aggressive because it’s much more difficult to eliminate those passing windows.  Moreover, there’s another factor to discuss:

The Blitz Bonus

A very successful blitz will result in a sack.  A sack dramatically swings the odds of a turnover (punts included) in the defense’s favor.  Now, comparing opposing QBs, against which ones do you think that’s most important to do?  I’ll give you a hint, it’s not Kyle Orton.

Against a great offense or great QB (frequently one and the same), the odds of allowing a 1st down are comparatively high.  For example, according to Pro-football-reference.com, the Denver Broncos faced 93 third downs needing 5 or fewer yards for a first down.  They converted 62.4% of those.

Now compare that to a bad offense, like Baltimore (ranked 30th by Football Outsiders).  The Ravens faced 96 third downs with 5 or fewer yards to gain.  They converted just 49% of those.

As you can see, getting to 3rd and less than 5, normally not considered much of a “win” for the defense, is still good enough to get you to 50/50 against a bad offense.  Assuming each opportunity is an independent event, the odds of the Ravens converting two consecutive such third downs is just 25%.

Hopefully your mental light-bulb just turned on.  Facing a Kyle Orton-driven offense, the Eagles were looking at a team much closer to the Ravens than the Broncos.  In that situation, just preventing a big play and forcing the Cowboys to convert a string of third downs was VERY LIKELY to produce a punt.

In other words, we didn’t NEED a sack!  The odds were already in our favor.  Conversely, if we had been facing the Broncos, the risk/reward equation flips.  That team is much more likely to convert a string of third downs, meaning the defense needs to do something to increase its odds.  Getting a sack is one of the only affirmative ways to do this.  In that case, the reward of getting a sack outweighs the risk of giving up a big play.  Without the sack, you’re likely to give up a long drive anyway!

Against a bad offense, though, that’s not the case.  It’s better to sit back, eliminate passing windows, and wait for the odds to shake themselves out.  By blitzing bad QBs, you’re making a foolish grab for upside that you don’t need.  Bad QBs will struggle to hit receivers that are even marginally covered, so why make it easy for them by making those passing windows larger?

Wrapping Up

Hopefully that illuminated things a bit more clearly.   Basically, against bad QB’s, the odds are already in your favor.  The reward of a sack (or forced incompletion), and the increased odds of a punt that come with it, are NOT worth the risk of the big play. In all likelihood, a bad offense will NEED a big play in order to score.  They simply won’t be able to string together a 12 play drive with a lot of 3rd down conversions.  Hence, the goal should be to get to third down as often as possible, and let the odds take effect.

Against a great QB, though, that’s not enough.  They ARE somewhat likely to string together 3rd down conversions, especially if their short yardage situations.  Similarly, they DO NOT need a big play to sustain a drive.  In that case, the risk of giving up the big play (which is worth relatively less to a great offense than to a bad one) is worth the associated reward of a longer yardage situation (which the defense needs to push the odds in its favor).

That doesn’t mean you never blitz a bad QB or always blitz a great one.  It does mean that you’re general pass rush strategy, particularly when it comes to sending extra pass rushers, should vary greatly depending on which QB you’re playing against.  Just saying “we’re a blitzing defense”, so we’ll blitz, is a very low-level strategy.  It’s far too simplistic, and sounds a lot more like a crutch than a well-thought out, adaptable and deployable strategy.

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15 thoughts on “Two-Factor Blitz Theory

  1. I agree that blitzing less is a good idea. Frankly, I have more an issue of HOW we blitz. Given that Barwin/Cole couldn’t sniff Orton, I’d have rather seen more double A-Gap blitzes with Barwin/Cole dropping. You’re still blitzing 5, but are attacking the coverage.

    Conversely, blitzing the far away slot CB or S 15 yards downfield needs to go. It never hits. It doesn’t fool the offense. It’s a wasted defender.

    FYI, Jim Johnson didn’t blitz that much. He simply knew what to call, when.

    • Agree completely about the types of blitzes used, however, that’s a separate topic. I’ve been pretty clear about my distaste for the CB and S blitzes. And the double-A gap blitz is a Davis favorite, despite being fairly easy to beat.

      • Given the discussion of variance and risk/reward, DB blitzes are far more high-variance. Blitzing both OLBs and rushing 5 is low-variance.

        The issue, IMO, is that when you can’t get pressure with 4, the natural tendency is to blitz. Doing nothing is not in a coach’s DNA.

      • True, doing nothing is surprisingly difficult (though it may be the right move). Spot on with the variance difference, which means DB blitzes should be used extremely rarely, and only when you absolutely NEED to make an affirmative play (like taking someone out of FG range or forcing a turnover).

  2. Davis has done more with this unit than I expected, so maybe he’ll grow into the role. But I am damned sick and tired of seeing a DB start his rush from 15 yards away only to see the ball come out long before he becomes a threat to the passer or watching a team that can neither rush the passer nor cover receivers. I don’t know if he calls too many blitzes, but too many of them are entirely ineffective.

    • Said in another comment, but analyzing the TYPE of blitzes is a completely separate issue (its a separate decision). Generally, the double-A blitz and the DB blitzes are much more risky than the LB blitzes, so they should be used less often. Have to find the data to see if that’s the case.

  3. I would say you are still oversimplifying the goal of a blitz. Several times blitzes worked in this game despite no one laying a hand on Orton, and despite Orton completing passes in those situations. The reason? When Orton saw blitz, he would immediately go to his hot read, which the Eagles did a good job of covering up and tackling before significant yardage could be gained. When a blitz forces a 5 yard completion on 3rd and 10, that’s a successful blitz for the defense.

    That’s also a good example of a blitz being used effectively as a “tool” to disrupt Orton, to use your terminology. Not only that, it was not something they came out doing in earnest in the initial series — thus I reject they idea that they were blitzing Orton out of “philosophical” necessity — but rather it was something they arrived at partway through the game after trying the base approach and finding it lacking. The issue to me here is, while Orton is not a great QB, the Cowboys had a huge talent advantage with their receivers vs the Eagles secondary which somewhat negates concerns about Orton’s accuracy, especially when he has time to throw.

    Lastly, I think there are some things regarding the Boykin interception play that need to be discussed a little further in this context. First, the Eagles are in a 3-3-5 nickel alignment with all three LBs (Kendricks, Ryan, and Barwin) showing blitz. However off the snap, only Barwin actually winds up “blitzing”. Ryans also rushes on a “green dog” because the RB stays in to block, but that doesn’t necessarily count. What Kendricks does though is really interesting and may have helped make the play. Instead of blitzing he drops immediately to double Witten over the middle. This is key because Orton starts looking at Witten immediately after the snap as his read because of the blitz, but the “blitz” is now no longer a blitz. Orton has to hesitate a split second, and this may have influenced his throw. This is just another example of blitzes and blitz looks being used as tools for confusion purposes, and there’s a reasonable argument that lower quality QBs may be more easily thrown off by these tactics.

    Also, if you watch the play live, Boykin has better coverage than you give him credit for. Even with a better throw he still is going to have an opportunity to make some sort of a play on the ball.

    • Agreed completely! Pressure and the illusion of pressure, do more than decrease the time that a QB has to throw. They confuse the QB and make his reads more difficult. Blitzing a good QB like Manning or Brees is a death sentence, because they can diagnose the resultant opening that’s created instantaneously. Blitzing a rookie or a rusty back up is more likely to yield a positive outcome for the defense, because it will cause hesitation and confusion and ultimately turnovers.

      Give almost any legitimate pro level QB plenty of time in the pocket while just dropping people in coverage and he will move the ball on your defense and accurately hit open windows. This is especially true when you have terrible DBs and the other team has extremely talented WRs.

  4. I think the logic you’re applying to this problem is very good, but the problem you’re applying it to is overly simplified. If you’re only considering guaranteed passing downs when the number of receivers is pre-determined, and the only goal of the blitz is to decrease time to find a passing window, then you might be right.

    But in live game situations you also have to factor in the blitz’s impact on running plays, confusing the line asignments, and confusing the QB’s comprehension of the coverage. A blitz can also keep an RB in the backfield and TEs on the line to help the protection. The skills of your potential blitzers matters too—Connor Barwin and Trent Cole are both better at blitzing than covering.

    The pros and cons of blitzing are not just based on the two factors you are solving for.

    • Conceded. Probably should have specified it, but clearly defensive strategy involves much more than the two factors I highlighted. So yes, I oversimplified, but my goal was to just explain in more detail why that particular aspect of the defensive game plan bothered me.

      Personnel matters a great deal, and if Davis is or isn’t confident in certain guys, it can shift the analysis significantly. I tried to stay at a general level so we wouldn’t have to include scouting reports on every guy. I should have just prefaced it by saying “all other things equal”.

  5. You also have to ask: Can you make the windows small enough that Kyle Orton can’t consistently hit them when not pressured in the pocket at all? If the answer is no (see our lack of defensive success playing coverage in the beginning half of the game) then all else is moot. You must confuse and hurry his decisions.

    • I think the answer is “most of the time”. Remember that not-blitzing does not mean NO pressure. It just means your only using 4 guys to minimize the QBs time. Sometimes that does lead to what is, in essence, unlimited time, but that’s very rare. Most of the time, one of those 4 guys gets there, it might just take them 1-2 seconds longer than if there’s a blitz.

      Any pro WR, given enough time, will create a window that even the worst pro QB can hit. That takes a lot of time though. If the front 4 really isn’t getting ANY pressure, then it changes the analysis.

      It’s more important to focus on the two factors first, then translate it into strategy. Each team’s personnel will be different and have different risk/rewards accordion to their strengths. In your example, the relative risk of NOT blitzing is much higher than what I’ve described as “normal”. That’s true of some teams. If that’s the case, balancing it against blitzing will tilt more heavily towards the blitz (basically what your saying).

      On Tue, Dec 31, 2013 at 4:18 PM, Eagles Rewind

  6. I like the model but it fails to account for how “cumulative pressure” impacts a quarterback’s accuracy. Blitzing a lot early and shaking up the quarterback can make them less effective later via them fearing phantom rushers. I know for the most part you like to avoid psychological implications in your analysis, but I assume you agree that pressuring a quarterback results in decreased accuracy?

    • Potentially. Still thinking that one through. Obviously it has an effect, no argument there. The question is what’s the best way to account for it in the model.

      It bleeds the factors together, which might make the model more accurate in theory, but does so at the expense of making it understandable. As you know, I’m of the opinion that simpler is better, and I’m glad to sacrifice a little bit of accuracy if it comes with a big gain in usability. Of course, to make that decision, we have to know how much accuracy we’re losing.

      Consider this Version 1, and expect either a full version 2 or at least an update with some modifications. Clearly needs a bit more complexity (maybe more resolution by breaking the 2 factors into sub-factors).

      On Tue, Dec 31, 2013 at 7:07 PM, Eagles Rewind

  7. A couple of other people noted it already, but I do want to refine the critique of your analysis. I think a lot of Chip’s philosophy is based upon trying to “speed up” the decision making process for the other team, making them doubt themselves and ultimately slowing them down (even if it’s for only a split second, in the NFL, that’s the difference between an incomplete pass and an explosive play). Having a blitz scheme with disguised blitzes seems to fit in pretty well with that overall philosophy. QB hits and pressures will speed up the QB’s decision making. The disguised scheme will make the QB hesitate a fraction of a second before making his decision. You sap the other team’s confidence, and it will result in poorer play. It’s sort of the flip side of Chip’s hurry-up offense; get the other team out of their comfort zone and the chances of making a big play increase, just on the basis of the other team starting to lose the ability to execute well, regardless of how your team is playing.

    It’s not a perfect defensive philosophy, but there probably isn’t one of those. You take the good with the bad, and hope that the good outweighs the bad. I think the dedication to a 2-gap 3-4 defense is premised on this philosophy, even though the talent on the team doesn’t really fill the roles of a 2-gap 3-4 very well.

    I also think that with the mismatched talent on defense, the Eagles *should* be running a high variance scheme – the “sweet spot” for that D in a low variance scheme is probably around 30 points against an average or better offense. They just don’t have the right talent to execute a 2 gap defense very well. They need to create turnovers and hope that the opposing offense helps beat itself. When they get more appropriate defensive talent for their scheme, they’ll probably back off the blitz some, but I’m guessing that it’s ultimately part of the overall philosophy of the team and is here to stay as long as Chip stays.

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