See how PFF College graded the USC defense vs. Notre Dame

USC had an odd night defensively Saturday.

The Trojans gave up 308 yards rushing in the 30-27 loss at Notre Dame, but 196 of those came in the first half (on 11.5 yards per carry!) and 69 came on the Fighting Irish's game-sealing penultimate possession. Meaning in the third quarter, when the defense allowed only a 52-yard field goal and forced a turnover on downs, it did find a temporary fix.

And it might have just kept building momentum if not for that fateful roughing the passer penalty on linebacker Palaie Gaoteote at the very end of the third quarter.

It was the what-if moment of the night, as USC had just cut its deficit to 20-13 and appeared to stop Notre Dame on third-and-6 as QB Ian Book threw incomplete. But Gaoteote was hit with the controversial 15-yard penalty as he finished his pursuit of Book and took him to the ground.

"Referees have very hard jobs and at full speed some calls are hard. I see it one way, another man may see it the other. You have to live with those calls and live with those calls as coaches," Trojans coach Clay Helton would say afterward.

Instead of the punt, Notre Dame drove for a field goal and in a 3-point game that was pivotal.

But an equal source of frustration was that back-breaking long Irish drive in the fourth quarter that took nearly 7 minutes off the clock and put the hosts ahead 30-20 with 3:33 to play.

If USC wants to lament something, that should be near the top of the list as the defense let Notre Dame convert on third-and-7 and third-and-10 (a 17-yard scramble by Book) on its way to the end zone. The Trojans have been susceptible to mobile quarterbacks all season and that weakness hurt them at the worst time Saturday night as Book rushed for 28 yards on that drive, including the 17-yard third-down pickup and finally an 8-yard touchdown.

Defensive line coach Chad Kauha'aha'a was apoplectic on the sideline in addressing his defensive line after that series.

"The first run was on us as a defensive line. We were out of our gap. Actually, both of them were," defensive tackle Brandon Pili said. "We didn't run the right call, so the A gap on the second play was wide open and the edge was open on the first long run. It was our fault, we have to go back to the drawing board. That's why he was a bit angry. We've just got to play better."

That said, the busts in rush defense in the first half were just as significant to the outcome of the game as USC never did climb out of that early 20-3 hole.

In explaining what went wrong, safety Isaiah Pola-Mao (and Helton) also seemed to highlight a fundamental flaw in the USC defense -- its reliance on sure tackling and gap integrity from a team that isn't especially good at tackling and that seems to have linebackers out of position too often.

"To me, I see if we take a couple plays away we're winning this game. They made their plays and we just didn't execute to our best ability," Pola-Mao said. "We're a gap-oriented defense. We missed a tackle, you're going to go at least 15 till you see the next guy. Like I said before, we just have to make our plays and execute."

Said Helton: "This is a very attacking defense, and when you do bring the pressures that you do the defense is all at one level and the next guy's about 15 yards back. It creates a lot of negative yardage plays, but also you have to be able to make your one-on-ones. When you miss them it creates explosives, so we've got to be better in that area moving forward the next six games."

Meanwhile, here's what the PFF College data shows from the defensive performance Saturday night:

RELATED: See how PFF College graded the USC offense vs. Notre Dame

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