I'll have to pay attention the next time ND plays a good team. Over a beer after the Temple game a few of us Boneyarders were talking about the days when Notre Dame used to be a good defensive team. Those were the days of Novosel and Mallory.
ND FG% allowed by year:
07-08 - 39.1%
08-09 - 38.6
09-10 - 41.0
10-11 - 36.8
11-12 - 36.1
12-13 - 37.7
13-14 - 37.8
14-15 - 37.6
15-16 - 37.7
16-17 - 39.3
17-18 - 40.9
The 2011-2012 starters were Diggins, McBride, Mallory, Novosel, and Peters. So yeah those were the best defensive years for ND in the recent past but the numbers were pretty consistent on D until last year.
Not sure why the drop last year. I'd guess it had to with having less depth. The class that departed prior to last year was Mabrey1, Cable, and Huffman. Without them, Mabrey2 and Ogunbowale had to play heavy minutes and carry the scoring both of which hurt their (not amazing to begin with) D.
Mabrey1 was not good on D but Cable and Huffman were so that probably played a part as well.
This year, everyone who had a chance to be good on D had their ACL tear, so that explanation is simple enough.