Let's have a little fun. Here are the stats of Michigan State's opponents in 2007:
UAB: 21/39, 265 yards, 1TD, 1 INT, 19.3 QBR; 32 rushes, 12 yards
Bowling Green: 32/51, 328 yards, 1 TD, 2 INT, 45.6 QBR; 25 rushes, 47 yards
Pittsburgh: 9/20, 118 yards, 0 TD, 2 INT, 10.5 QBR; 38 rushes, 207 yards
Notre Dame: 11/20 118 yards, 0 TD, 0 INT, 6.2 QBR; 35 rushes, 117 yards
Wisconsin: 17/25, 267 yards, 2 TD, 2 INT, 43.0 QBR; 52 rushes, 214 yards
Northwestern: 38/49, 522 yards, 5 TD, 0 INT, 96.0 QBR; 34 rushes, 91 yards
Indiana: 13/19, 211 yards, 1 TD, 0 INT, 56.3 QBR; 17 rushes 22 yards
Ohio State: 15/23, 206 yards, 2 TD, 1 INT, 69.4 QBR; 47 rushes, 229 yards
Iowa: 5/15, 64 yards, 1 TD, 0 INT, 11.4 QBR; 44 rushes, 230 yards
Michigan: 18/33, 221 yards, 4 TD, 1 INT; 51.4 QBR; 30 rushes, 100 yards
Purdue: 29/45, 362 yards, 2 TD, 2 INT, 67.8 QBR; 25 rushes, 173 yards
Penn State: 16/37, 188 yards, 1 TD, 0 INT, 33.9 QBR; 40 rushes, 167 yards
And now Nebraska's defensive stats through 4 games so far (this is going to be painful):
BYU: 28/46, 379 yards, 2 TD, 1 INT, 68.5/87.6 (Hill/Mangum) QBR; 26 rushes, 132 yards
South Alabama: 26/45, 313 yards, 1 TD, 1 INT, 42.5 QBR; 24 rushes, 19 yards
Miami: 25/42, 379 yards, 2 TD, 1 INT, 67.6 QBR; 33 rushes, 132 yards
Southern Miss: 26/42 447 (*cough*) yards, 2 TD, 0 INT, 72.1 QBR; 23 rushes, 11 yards
So as you can see, those aren't quite similar stats that teams put up against the Spartans in Narduzzi's first year implementing his similar defense at Michigan State. Now you can take this one of a few ways:
1. It's easier for teams to pass the ball in 2015 than 2007, and there's been a greater emphasis by teams to throw the ball more. I think it's pretty safe to acknowledge that offenses are scoring more points in today's version of the game than they scored in older versions. Just the way the game is called and officiated gives offenses advantages over the defense, and good teams are taking advantage of that. Despite the changes in the game since 2007, there's not much of a difference in how many yards a majority of teams pass for between 2007 and 2014. In 2007, a majority of college teams ended the season with 2155-3685 yards whereas in 2014 a majority of teams ended the season with 2146-3782 yards.
2. Perhaps the teams we faced were just pass heavy teams. It's true, the Big Ten is a run-heavy conference, and perhaps our secondary won't be asked to do as much work as they have during the past 4 weeks. So perhaps we won't be seeing these kind of performances because our conference opponents will stress running over passing and will play into the strength of our defense. I looked at the run/pass % of teams on our schedules, just to see if we just had the misfortune of coming across pass-heavy offenses.
BYU after 4 games, sits at 54/46 pass/run%: against Nebraska it was 64/36 pass/run%
USA after 3 games, sits at 51/49 pass/run%: against Nebraska it was 65/35 pass/run%
Miami after 3 games, sits at 54/46 pass/run%: against Nebraska it was 56/44 pass/run%
So Miss after 4 games, sits at 53/47 pass/run%: against Nebraska it was 65/35 pass/run %
So the only game where the pass/run splits wasn't significantly different than the team's season average was against Miami, which means that teams were able to notice that they were able to get Nebraska through the air that they were comfortable enough abandoning their identity. If Nebraska's secondary play doesn't improve, more teams--regardless of how pass or run-heavy their offenses are, will be comfortable in abandoning their offensive identity as well. Let's see their pass/run% so far in this young season:
Illinois: 51/49 pass/run%
Wisconsin: 48/52 pass/run%
Minnesota: 46/54 pass/run%
Northwestern: 27/73 pass/run%
Purdue: 50/50 pass/run%
Michigan State: 42/58 pass/run%
Rutgers: 43/57 pass/run%
Iowa: 43/57 pass/run%
So more teams in the Big Ten favor the run game over the pass, that's not really surprising, and could mean that our defense may improve upon entering conference play. Although I'm not sure if teams will stay true to their identity and tendencies or if they will abandon that and pass more because of how porous our secondary has been in the early going.
Nevertheless, this defense--the secondary especially--has a lot of work to do if we want to get through this season respectably.