Michigan State had a rock solid defensive success rate on standard downs (they ranked 16th in the country in Standard Downs SR+), and they laid down and went conservative on passing downs (they ranked 106th in Passing Downs SR+). The difference of 90 spots between those two categories is the highest on record in the "We have play-by-play data for it" era.
Biggest Differences Between Standard Downs SR+ and Passing Downs SR+ (Std Downs > Pass Downs) (2005-10)
1. 2010 Michigan State (90 spots - 16tth on standard downs / 106th on passing downs)
2. 2009 Minnesota (90 spots - 25th / 115th)
3. 2008 Arizona State (78 spots - 12th / 90th)
4. 2010 Minnesota (77 spots - 36th / 113th)
5. 2010 Fresno State (76 spots - 17th / 93rd)
6. 2008 Air Force (76 spots - 23rd / 99th)
7. 2010 Kansas State (72 spots - 47th / 119th)
8. 2005 Tulane (70 spots - 37th / 107th)
9. 2010 South Florida (70 spots - 27th / 97th)
10. 2007 Boston College (69 spots - 24th / 93rd)
If there's a positive spin here, it's that four of the five non-2010 teams on this list saw improvement in their overall defensive ratings the next year. In a way, this makes sense. Low success rates on passing downs suggest that you are backing off and playing conservatively ... which, among other things, suggests that you might not trust your secondary very much (whereas you trust your front seven enough to attack quite a bit on standard downs). If that is because they are young, then the next year they are probably going to be quite a bit more experienced.
(Of course, this doesn't necessarily apply to Michigan State, which fielded three second-team all-conference defensive backs in Marcus Hyde, Chris L. Rucker and Trenton Robinson. Corner Darqueze Dennard was a freshman, but still.)
So what do we have at the other end of the spectrum?
Biggest Differences Between Standard Downs SR+ and Passing Downs SR+ (Pass Downs > Std Downs) (2005-10)
1. 2008 Texas Tech (91 spots - 101st on standard downs / 10th on passing downs)
2. 2006 New Mexico State (89 spots - 111th / 22nd)
3. 2010 New Mexico State (75 spots - 108th / 33rd)
4. 2010 Penn State (73 spots - 84th / 11th)
5. 2007 Hawaii (72 spots - 99th / 27th)
6. 2010 SMU (72 spots - 89th / 17th)
7. 2006 Indiana (71 spots - 99th / 28th)
8. 2007 UNLV (71 spots - 96th / 25th)
9. 2010 Central Michigan (68 spots - 111th / 43rd)
10. 2010 Nevada (68 spots - 105th / 37th)
Of the five non-2010 teams on this list, three regressed the next year, two rather significantly (2007 Hawaii, 2007 UNLV). If we were to stretch the list out further, nine of the top 13 teams on this list regressed the next year.