The #1 thing Golden does is take away a quarterback's ability to easily diagnose what type of coverage we are going to see. There's a lot of scheme involved, but it starts with personnel selection.

Remember what some of the things are an OC will do to help a quarterback:

+ against zone, they'll call plays that "stretch" a given defender into a no-win situation. Think of a "smash" concept (hitch by an outside receiver, corner by an inside receiver) against a Cover 2 corner: if he drifts back in such a way that he might play the corner the hitch will be open and vice versa

+ they'll call man beaters to one side of the field and zone beaters to another, with obvious #1 reads in either scenario

+ They'll us motion to a) get the defense to declare whether it's in zone or man coverage and b) create matchups wherein a poor man defender is matched up with a quick receiver (to create an obvious "first read" type matchup)

To counteract those two "go to" tricks, it all starts with having guys who can play man coverage.

The more guys who can man-cover a) the less able an OC is to give his QB easy reads and, importantly, b) the more able Golden is to disguise/bluff. That is, a QB can't by process of elimination look at the defense and say "Well, I know it is X defensive scheme, because if it were Y or Z, that would mean they'd be leaving the free safety in man coverage, and they wouldn't do that . . . or if they do it's easy money." We regularly put at least five dudes on the field who can lock up man-to-man. We don't always have all (or many) of them in man-to-man, but we could and you've got to spend precious time post-snap diagnosing what is what.

Getting those many good coverage guys organized lets you do a lot, even within a play. Look at the last play against Louisville:

https://youtu.be/2G4BSXReYzw?feature=shared&t=9051

ND is showing (imo) a relatively common defense called "Cover-1 Robber." Essentially, everyone is in man to man but there is one safety deep (Watts) handling the deepest threat and one safety in the short zone (Shuler) trying to read the quarterback and "Rob" anything over the middle.

Louisville, it looks like, is running a concept in which they are sending a shallow crossers horizontally in the intermediate zones and a deep crosser coming from the field side to the boundary side. They probably felt pretty good when they saw how ND lined up. The thought would have been that Shough could look first to the crosser moving from the field slot into the boundary (picked up by Rod Heard), and this read would cause the robber (Shuler) to jump that route. The robber accounted for, Morrison would have the very difficult task of chasing a crosser all the way across the field. Then, even if Morrison somehow were all over that, then the nickel (Clark) would have the very, very difficult job of tracking a deep crosser all the way across the field. One of those two things are going to be open against a C-1 Robber look, you have to figure.

Look at this screenshot: https://youtu.be/2G4BSXReYzw?feature=shared&t=9082

At this point, you have to believe Morrison is cooked and Shuler is coming down on the right to left crosser (Heard's guy). But that's not the defense! It's not Shuler who is the Robber, it's Morrison! Shuler is picking up the left-to-right crosser in man, and, having started the play several yards inside of the crosser, has great leverage and can cover man really well. That route is dead. Shough then looks to the deep crosser but Morrison has drifted back to rob that, double covered! Shough doesn't know what the hell to do. He looks around, wildly pump fakes to nothing a couple of times, and decides to just launch it deep, where Moore and Watts are double covering a guy who is likely never designed to get the ball on this play anyway. Game over.

Now, this is a lot of pixels spilled about just the pass defense, but that's appropriate. It's what ND actually cares about much more than overloading against the run. The confusion generated does help with the run game as well, though. By making it difficult for an offense to be sure of what they are seeing, you make it very unlikely that every single blocking call is going to look exactly clear to all the blockers. You might not always win at the point of attack, but you are very likely to get an unblocked guy (a "free hitter") to the point of attack within a few yards of the LOS. Fortunately, our free hitters have done a great job tackling, but you have seen examples when they miss and it becomes an explosive (Shuler on the long run by Stanford
in the first quarter this year, DJ Brown against Clemson and Louisville last year, Watts vs. Ohio State last year).

All in all, though, it's a top notch defensive scheme. Strategically well chosen, players developed extremely well towards its goals, obviously well installed and exquisitely executed.