Thinking about this for awhile now, but especially as we are looking for a defensive coach again with Mattison's retirement. Also, I think this fits Coombs better, too.
Seems to me that even Day has massive respect for Northwestern's style of defense. He says they make you earn every inch. These are 2-star and 3-star players for the most part, yet they made Justin Fields play his worst college game. It's essentially a Cover-2 base look that can also disguise Cover 3 and Quarters. Mostly, they play zone. When they have more 3-stars or more seasoned players, it's a tough/disciplined/simple defense. They're very strong at limiting explosive pass plays (which sort of define the best offenses in CFB now).
As the GOAT Saban says, good defense no longer beats good offense. College football has flipped. Of course, most defenses are multiple, but your base defense matters, especially in helping guys play fast because it's simple.
After the 2012-2013 seasons, Urban when Urban saw his DBs get beat underneath a lot, he looked at what Dino did with lesser talent at MSU with Quarters, and tapped Chris Ash to do it here. Result = National Championship.
After the failed Schiano/Grinch year, Day hires Jeff Hafley to run Pete Carroll's single high, cover-3...Resulting in one of the top defenses in the country. However, all 4 defensive backs are NFL backs and older/seasoned players. That includes 2 first round corners, rookie starting safety in Jordan Fuller, and soon to be early round pick slot corner Shaun Wade as well as mister jack-knife Bullet soon to be early round pick Peter Werner. Oh yeah, defensive rookie of the year Chase Young also made their jobs easy. Also, Schiano's defenses looked great early because he had Nick Bosa on the DL, Malik Hooker, Marshon Lattimore, and Denzel Ward at corner. Coincidence?
There will be seasons where we have seasoned 4/5 star, future 1st or early round players in the defensive backfield or on the line. 2020 was NOT one of those seasons & we paid for it.
While single-high, Cover-3 seems to work best with that level of talent, when we have more youth or just aren't that talented, it seems like going the Northwestern route is better. It would seem to set younger, less experienced players up for more success.
I also think that going the Northwestern route when we have first round talent would be excellent, too. Can you imagine players of our talent level playing their defensive scheme? I don't see the downside, whereas, if you don't have the talent/experience to play single-high, cover-3...it looks like what we got against IU, Clemson, or Bama.
What do you think?