Lets see how they got to that 15th ranked pass D.
Navy - 2/4 20 yards - So basically didn't try to throw at all.
Va Tech - 199 yards - Again not a throwing team and were running clock most of the 2nd half
UC - 352 yards to Gunner Kiel, probably the best QB they faced this year and is not even close to Mariotta
Kent - 76 yards. Completely out matched in every aspect
MAryland - 244 yards. Two QBs for Maryland, Brown started and was playing hurt before being removed
Rutgers - 194 yards. Pedestrain QB, Pedestrian numbers
Penn St - 224 yards. Right at Hackenberg's season average
Illinois - 137 yards. 2nd and 3rd string QB on a bad team
Michigan St - 358 yards passing for a run first offense
Minnesota - 85 yards. 2x's as many rushes as passes in a cold, windy game
Indiana - 114 yards. Freshman QB that wasn't even supposed to see the field and only avg 86 yards a game
Michigan - 233 yards to a run first QB. Also his season high in yards thrown.
Wisconsin - 187 yards for a bad QB. Over his average. Outlier of a game since it was well in hand early?
Alabama - 237 yards. Just below season avg for a team that is run first.
The most pass happy team they faced was Cincy who put up 352 yards 4 Tds/0 int and had no run game to speak of. Kiel and Cook put up 350 yards and are not even close to the runner (or thrower for that matter) that Mariotta is. It would be hard for any halfway decent defense to not put up these type numbers against these type teams. This stat is hugely inflated due to games against Navy, Kent st, Minnesota and Indiana who put up bad yardage numbers against everyone.