The nutty Michigan coverage isn't so much about Harbaugh as it is a signal to the Big Ten that Fox wants to party.
Notre Dame has a very good defensive line, possibly great. If they still had Aaron Lynch holy pants man. They don't, but Tuitt is a 300 pound pass rusher, Nix is hard to move, and their Kapron Lewis-Moore/Prince Shembo combo at the other DE is a quality option. They've been making a lot of plays so far, and some of them against Lewan, who has a bunch of NFL hype and has shut down virtually every DE he's ever gone up against, including guys like Adrian Clayborn.
So Michigan was up against it against the Irish. They compounded those troubles with a spate of seemingly bizarre play calls that made it even harder for Michigan to execute since they often left key players unblocked, with the results you saw.
Here's a two yard run in the second quarter. It's first and ten on the first play of Michigan's first drive after the Smith interception. ND comes out showing a four-man front with one-high coverage, but will shift into their standard 3-4. Zeke Motta, currently 16 yards off the LOS, will approach the LOS for an eighth run defender against eight players in the box.
Post-shift, this is about standard for ND. Note that the secondary is showing extremely soft man coverage on the receivers, which is par for the course when you are in cover zero with three converted offensive players. Or at least, I'd imagine it's par for the course if anyone else ever did this.
Now, you may be thinking "AAAAAH DAMN AAAH BUBBLE." I am too. The defense is allowed to align like this because Michigan won't take a shot at that gooey soft edge. Constraint plays constrain what a defense can do, simplifying life for QBs. Here we've got a play, and it's a run despite the D showing a cover zero look.
On the snap it's revealed to be an inside zone play…
…but Lewan does something unusual by flaring out to go block Shembo as Denard reads Lewis-Moore. Meanwhile, look at Toussaint's upfield angle of attack:
This was supposed to be a midline type read. When ND showed a four-man front, Nix was shaded outside of Mealer. He would hit the frontside A-gap, allowing Barnum to release into the second level. Instead he's head up on the center and fights back, forcing Barnum to try and deal with him.
What Michigan thought it was doing
Meanwhile, Lewan's flare out on Shembo was supposed to be useful. Instead he's blocking a contain guy on a run up the middle. Lewis-Moore is not tearing up in a gap like a one-gap DL would but coming upfield under control.
So instead of a quick hit that got Michigan past the DT they get this:
Which is two yards thanks to an unblocked LB in the middle of where your belly is supposed to go.
This Looks Familiar
Denard's second interception is a terrible throw helped along by a totally unblocked Te'o as Barnum tries to help on Nix.
Terrible throw and all that but also not a shining example of coordinator mastery. This is a position to fail in, when you can't step into your throw because you'll get hit if you do so.
Things and Stuff
RB angle gives you the intended hole. Look at how vertical Toussaint is going. This is designed to go backside.
Checks: none. Once ND shifts to the three-man front, this play is in trouble, and once Motta slides down you're up against zero safeties. This would be a nice time to check. To what? Well, you are maybe probably getting some yards if Lewan changes his assignment and releases directly into that LB, or, you know…
…that OLB has eyes only for the backfield, so you've got one guy within twelve yards of the slot receiver. Who isn't a slot receiver, sure.
Since this was the first play of the drive I assume there was time to do this after the shift; nothing comes. This might be on Denard, or there just might not be a check for this. Rodriguez took that check burden onto himself with those plays where Michigan would call for a snap and then everyone would look to the sideline.
Constraints: none. A little later Michigan will block a QB sweep well but Motta will show in the hole as an unblocked eighth guy. Denard will abort and get three. ND again went cover zero with pudding soft outside coverage:
They're sitting out there waiting to give you their money! It's not the stupid little bubble itself that helps—though the yards from 2-8 averaging about 6 aren't bad—but the things that the defense can't do because they can't align with their secondary in Bolivia and bring down a run defender that erases your numerical advantage.
This alignment cannot be allowed to exist without a quick easy throw that invalidates it. Have we mentioned that both corners are converted offensive players? And one is a freshman?
Oy OL. Note that Nix not only drew a double but ripped through it to the backside hole, and that Tuitt has gotten inside of Schofield with ease. It may have been possible to get some yards here by getting Nix sealed and hitting a gap further to the playside, but none of that happens. I haven't gotten to the bit where Michigan just grinds on them yet, but so far there have been a lot of plays like this where Michigan OL get nowhere with their guys.
Why are we running a play that seems designed to go at a 4-3? ND will go to it but they are a 3-4 at heart and when they show a four man line it's usually short yardage or a passing down. I would expect an incoherent play like this to fire off when ND is giving Michigan a 4-3 curveball instead of the 3-4, especially after Michigan spent two weeks preparing exclusively for this defense. That Lewan flare-out is deadly to this play because Barnum has to help on a NT who is not shaded—and is rarely shaded. Meanwhile that guy on the edge is not a threat to Toussaint. RPS –1.