I believe we heard afterward that Shields played it correctly, but I don't recall whether that was the official word or the word leaking out of the locker room. If it was the correct technique, then it puts the safety in a tough spot. And that may be why a Capers D needs vets. The safety, if we assume there is not supposed to be linebacker help, needs to read his first key and then the QB or the route. And I think it was single safety so he has a lot of ground to cover.
But that is just an evolutionary step to the game between defense and offense. The Packers had engineered a single high safety defense committed to stopped Lynch to the strong side of the offense. Seattle found a way to pull the linebackers into the LOS with a play fake (the read option) and when they or the safety bite, he rolls out to run or pass. They get to isolate a player, make him choose and then take advantage of the choice. You won't see that D against that personnel formation again.
Georgia did the same thing to Alabama the previous year. Saban is not a man given to designing unsound defenses but he got caught by the same damn play. The play is indicative only of the offense getting a one play advantage over the D.
Much more problematic are two other questions wist asks, both of which are tangentially related to this play.
1. Are Capers defenses regularly over engineered to stop certain kinds of plays and therefore constantly vulnerable to counters?
2. Does the over-engineering come from Capers tendency to be a Mad Scientist or because he is covering flaws in his defense? I know Capers board and internet rep is that of mad scientist, but he isn't Ryan or Gregg Williams. He does design new blitzes, but his most common calls are pretty standard stuff. He does not invent new defenses every week. He tweaks assignments. He follows McCarthy's dictates that he change the strength of his D by substituting personnel rather than invent a new scheme. *
I think he is covering for flaws. The switch to the 4-3 and the new bodies on the line have introduced new variability that is hard to account for and Fritz could be right, they may want more penetration though I am not sure. But just as gap discipline was great to start the year last year, its been piss poor this year. And it is often, though not limited to, the middle of the defense. Now the why they can't be consistent is troubling.
* I would bet that whatever threshold the D staff changed after '09 (down and distance and tendency) to determine when to use nickel rather than base happened at McCarthy's urging. He figured they would always be in shootouts so play pass defense first. So put the nickel group in earlier to counter it. As for new schemes, we have seen Psycho and amoeba defense, but that is just window dressing on a standard pass D or fire zone, making the O line guess who and how many are coming. That is less scheme and more personnel to me.
I don't like Offensive based HCs telling their defense what to scheme. Scout, hand over confidential data? Sure. But don't muck up the works with new top-down edicts. The defense is designed from the bottom up to adhere to principles and that informs everything from practice to play calls and player acquisition. When I watch the Packers D, I see a mishmash of junk and very few doing their job well. It doesn't look well organized at all in the front seven. Its the exact opposite of how the year started last year.