DIACO
2010 23rd PPG - 50th ypg - 8-5
2011 24th PPG - 30th ypg - 8-5
2012 2nd PPG - 7th ypg - 12-1
2013 27th PPG - 31st ypg - 9-4
ELKO
2017 32nd PPG - 44th ypg - 10-3
LEA
2018 27th PPG - 49th ypg - 6-0
I know these stats are simplistic and the styles of play are different but Bob Diaco was a good defensive coordinator under Brian Kelly. That’s just a fact. There were some things that fans didn’t love and I think it was good for both parties that he move on to a head coaching job, but to say he was a bad coach or didn’t know defenses is just disrespectful. The dude can coach.
Diaco basically stopped recruiting for two full classes, and has a unique personality. He created massive depth issues that should never happen at Notre Dame. After flaming out at UCONN and Nebraska he kicked the tires on coming back to ND as a position coach or analyst and we weren't interested.
While his defenses performed well on a vanilla stat basis, here is how they ranked in S&P+/FEI respectively --
2010 - 10th/11th
2011 - 11th/18th
2012 - 8th/14th
2013 - 48th/49th
That's very good... consistently in the top 10-20 range... but the wheels were already falling off the cart by 2013 on account of talent depletion. He signed a good class in 2011, and then the lack of recruiting success in the '12 class and '13 (especially at linebacker and defensive tackle) set the table for the struggles over the next three seasons. These talent/recruiting issues were compounded by BVG being as bad as it gets as a coach and the Frozen Five thing and other nonsense.
For reference, this year's defense currently ranks 5th in S&P+, better than any Diaco defense. The primary issue with Diaco's scheme is that kids don't want to play in it and he couldn't recruit to it. Everyone likes the rush end spot in the 3-4 but no one likes being the block-eating NT. Nobody likes being the gap plugging DEs. And there are very few 6'5" 280+ DE prospects to choose from coming out of HS. There are also very few 6'3" 240+ LB prospects to choose from. No one likes playing super soft zone coverage every down as a CB.
I think he could be a good fit at a school like Kansas State that does a ton of JUCO recruiting and where he can focus primarily on guys who are physical fits without a lot of options. But he has proven he either can't or doesn't want to recruit HS prospects.