It doesn't take a deep dive into the advanced metrics to say that USC's defense has underwhelmed and underachieved this season.

The Trojans ranked 71st nationally in total defense at 382 yards per game allowed -- up from 369.7 last year -- and 79th in scoring defense at 27.3 points per game allowed (up slightly from 26.0 last year).

But the trends indicate those numbers could turn out much worse as the schedule stiffens up.

A Washington State team playing most of the game with a walk-on QB mustered only 279 yards against the Trojans while a moribund Colorado offense generated just 242, helping those overall numbers.

Meanwhile, Oregon State (535 yards) and Utah (486) feasted against USC.

With No. 13 Notre Dame awaiting the Trojans this week in South Bend, Ind., and decent enough offenses from Arizona State (433.6 yards per game), UCLA (425.1), Cal (407.0) and BYU (406.6) still on the schedule, the defense will have to play much better across the board to even maintain the numbers it has averaged thus far. (The Fighting Irish actually rank a lowly 87th nationally at 367.8 yards per game, for what it's worth).

The intrigue on the defensive side moving forward is whether the coaches decide they're ready to see what their younger players can do in larger roles with so many veterans struggling week after week.

To paint a fuller picture of all of that, we go deep inside the PFF season grades, advanced stats and snap counts to break it all down, including taking a look at the Trojans' redshirt possibilities on defense.

RELATED: Analyzing the midseason PFF grades and snap counts for USC's offense