On the whole, Louisville's defense was exceptional in Year 1 under coordinator Todd Grantham -- a neat trick given that (A) Grantham was installing an entirely new scheme, and (B) he was doing it largely with players recruited by Charlie Strong.

But dig a little deeper into the numbers and there's an odd dynamic at work -- particularly when it comes to the run defense.

In Louisville's first eight games of the 2014 season, the Cardinals' defense allowed just 2.24 yards per carry on the ground and just one rushing touchdown (none by running backs).

In Louisville's last five games, it allowed a whopping 4.5 yards per carry and 11 rushing touchdowns.

So how did a defense that was dominant through mid-October fall off the map down the stretch? And what does that mean for the Cardinals' defense in 2015?

The most obvious answer is that the competition got better. In the latter half of the season, Louisville faced Florida State, Boston College and Georgia, with Nick Chubb having a field day in the Belk Bowl. A marked decline in numbers was inevitable.

If we compare Louisville's performance to its opponents' averages, we see that actually does account for a portion of the decline. The Cardinals held all but one of their FBS opponents below their season average (FSU was the exception), but we also see the difference was less pronounced down the stretch than it was early in the season. In those first eight weeks, Louisville was roughly 42 percent better than other defenses against the same opponents. In the final five weeks of the season, it was just 8 percent better.

And, not surprisingly, Louisville isn't quite satisfied with those numbers.

"It makes us want to work way harder, condition in the weight room so our bodies last longer into the season," linebacker James Burgess said. "Later in the season, players were beat down and that affected us on the defensive side."

That's one potential explanation. Burgess started every game, but he was banged up by season's end. Lorenzo Mauldin was hurt against Florida State, missed the next week and dealt with a nagging hamstring injury the remainder of the season. Not coincidentally, this is when things began to nose-dive on defense.

"When you launch yourself into the ACC, where you have to work to catch up a little bit is depth," said Grantham, whose defense also saw more designed runs overall down the stretch. "As injuries happen, you have to have enough depth to continue playing at the level you were. That's something we've tried to solidify."

In particular, it seemed the lack of linebackers who could set the edge consistently was a major cause of Louisville's late-season struggles.

On runs inside the tackles, Louisville made initial contact at roughly the same point both early (1.7 yards before contact) and late (1.9) in the season. But on the outside runs, things got noticeably worse. In the early games, first contact occurred an average of 2.1 yards beyond the line of scrimmage, but in those final five games, that number climbed to 3.3, according to ESPN Stats & Information, while the average yards after contact nearly doubled.

Grantham also changed his approach a bit, with the average defenders in the box increasing from 6.5 yards per run through eight games to 7.2 during the final five, per ESPN Stats & Info.

In other words, there was a lot at play here. A lack of depth at linebacker -- particularly on the outside -- hurt Louisville. Poor tackling made things worse. Better opposition took advantage of both.

In 2015, the Cardinals return the bulk of their front seven, but Mauldin is an obvious exception. That likely puts the focus squarely on former TCU star Devonte Fields and junior Keith Brown, who moved from inside to outside this spring, to perform at a high level in 2015.

The secondary shifts a bit, but the addition of Josh Harvey-Clemons certainly adds a physical presence at nickel and safety, and another year in Grantham's system should help improve the tackling fundamentals overall.

And the tests will come early, too. Louisville gets Auburn in Week 1, as big a challenge to the run defense as it's likely to get all season. Clemson, Florida State and Boston College soon follow, with James Conner and Pitt waiting in late November.

The bottom line here is Louisville's defense needs to look a lot more like it did early in the 2014 season if it wants to be a legitimate Atlantic contender in 2015. The trends don't offer a ton of optimism, but the personnel still looks solid. The onus then shifts to Grantham to get his unit ready for what's in store.

"The players who have been here have done a good job of learning our system, and we've been able to play fast," Grantham said. "But even the guy that has played and had experience can get a little bit better, and the guys learning the system gain knowledge that allows them to play fast. You're always learning as a player, and there are always ways to improve your craft. So you're really starting over again and go through the whole process the same way."