USC hasn't faced a defense yet this season that presently ranks higher than 40th nationally (Arizona State, No. 40).

In fact, the Trojans have faced mostly bad defenses -- San Jose State (93rd), Nevada (133rd, dead last in the FBS), Stanford (127th), the aforementioned Sun Devils, Colorado (130th) and Arizona (47th).

That all changes Saturday as the No. 10-ranked Trojans (6-0) visit No. 21 Notre Dame (5-2) in South Bend, Indiana (4:30 p.m. PT on NBC).

The Fighting Irish have had their struggles offensively of late (more on that momentarily), but they have been an elite defense, ranking 12th nationally in yards allowed (279.4 per game) and 15th in scoring defense (15.9 points per game).

"Their linebackers are super aggressive. They're downhill guys. They have some great plays on film where they're making contact with people and just knocking people backwards, so we've got to be ready for that," USC offensive line coach Josh Henson said. "Obviously, because those guys are so good they like to blitz them. We've got to be ready to pick up those blitzes. They're big and strong inside, they use their hands really well on the interior. They get a lot of disruption from interior pass rush, so we've got to be ready for that. But overall, I think one of the most impressive things about them is they just play extremely hard.

"They run to the football, they swam and chase and all those things you want your defense to do. We've got to go match their intensity. Looks like we're going to have great weather (sarcasm) in South Bend, so you know, it might be one of those games that whoever can punch the other one with enough body blows is the one that wins at the end."

USC comes into the game as the top scoring offense in college football (51.8 points per game) and fourth in yards (523.3 per game), but the Trojans had a tough time getting started against Arizona last week and now face by far their toughest test of the season.

Let's take a closer look at the matchup ...

RELATED: Opposing Perspective: Notre Dame insider Tyler James breaks down the Fighting Irish

Coach: Marcus Freeman, 2nd season (14-7, including 1 game as interim HC)

National ranking: No. 21

Series history: Notre Dame leads 50-37-5 (50-38-5 if counting USC's vacated 2005 victory). The Trojans have lost their last five trips to South Bend, the longest such streak since dropping seven straight from 1983-95.)

Familiar faces: Notre Dame running backs coach Deland McCullough previously served as USC’s run game coordinator/running backs coach in 2017.

Vegas odds: Notre Dame is a -3-point favorite and the over/under is set at 60.5.

Statistical comparison:

The Fighting Irish landed one of the biggest transfer additions of the offseason in prolific Wake Forest quarterback Sam Hartman. And yet, their passing attack has not been especially dynamic, in part because of more conservative play-calling than Hartman enjoyed at Wake Forest, but also because the receivers haven't been dynamic as a unit. Mitchell Evans (22 receptions for 343 yards and 1 TD) leads a balanced group that hasn't had much of a clear hierarchy emerge yet with Jayden Thomas (15-228-1), converted running back Chris Tyree (14-293-2), freshman Rico Flores (14-154-1), Jaden Greathouse (12-166-3), Tobias Merriweather (8-164-1) and tight end Holden Staes (8-139-4) all in the mix. Merriweather was supposed to be the top downfield threat, but that hasn't materialized as hoped.

Notre Dame leans more heavily on its rushing attack with established star back Audric Estime (692 yards, 7 TDs on 6.6 yards per carry) leading the way while freshman Jeremiyah Love (257 yards on 7.1 YPC) is starting emerge as well. But the Irish were shutdown on the ground last week in a 33-20 loss at Louisville, totaling just 44 rushing yards (1.6 YPC) after factoring in lost sack yardage. Estime managed just 20 yards on 10 carries as Louisville loaded the box against him.

The Irish have a standout left tackle in Joe Alt, but they've had some issues on the interior of the line and rotated at right guard between redshirt sophomore Rocco Spindler and redshirt freshman Billy Schrauth. Redshirt sophomore right tackle Blake Fischer, a former five-star recruit, has also struggled and gave up 5 pressures and 2 sacks last week.

Notre Dame has managed just 14, 21 and 20 points, respectively, the last three games as first-year offensive coordinator Gerad Parker, who was the team's TEs coach last season, has come under scrutiny.

The strength for Notre Dame is in its secondary, as the Irish allow the third-fewest passing yards per game in the country (146.6). That's skewed a bit by some of the opponents they've faced, like ground-oriented Navy (which only completed 3 of 7 passes for 43 yards), but only two opponents have even mustered 150 passing yards against this defense -- NC State (260) and Ohio State (240).

Notre dame has 6 interceptions from a variety of contributors in safety Xavier Watts (2), safeties DJ Brown and Ramon Henderson and cornerback Benjamin Morrison with 1 each. Morrison has a team-high 5 pass breakups, while fellow corner Cam Hart has been pretty stifling so far in allowing only 5 completions for 84 yards over 16 targets, per PFF, with 3 pass breakups.

Interestingly, Notre Dame's leading tackler is nose tackle Howard Cross III, who has 42 tackles, 5 tackles for loss, 2 forced fumbles and a team-high 20 pressures while defensive tackle Rylie Mills has 16 pressures.

Redshirt senior middle linebacker JD Bertrand has 41 tackles despite missing a game, and veteran defensive end Javontae Jean-Baptiste has 15 pressures and 31 tackles.

Something has to give between USC's third-ranked passing offense and Notre Dame's third-ranked passing defense. As noted, the Irish haven't allowed more than 260 passing yards in any game and are keeping opponents to a collective 50-percent completion rate. Meanwhile, Heisman winner Caleb Williams is completing 71.7 percent of his passes for 1,822 yards (303.7 YPG) , 22 TDs and 1 INT.

Notre Dame gave up 5 sacks last week and now faces one of the most productive pass rush units in the country as USC is tied for 7th nationally with 3.67 sacks per game.