Monte Kiffin was ousted as USC's defensive coordinator after three seasons. Clancy Pendergast lasted one tumultuous but fairly successful season before he was swept out in a coaching turnover.
Now, after embarrassing defensive performances in losses to Boston College and Arizona State, the target is Justin Wilcox.
USC gave up 452 yards rushing at Boston college and 510 yards passing in last week's defeat by Arizona State at the Coliseum.
To make matters worse, the Arizona State game ended with confused USC players failing to go for the ball on a last-second, game-winning Hail Mary pass.
Wilcox accepted blame for a communication breakdown during the final sequence. He described the defense's play this season as "schizophrenic."
The pressure on Wilcox will increase if USC's defense struggles and the Trojans lose again Saturday against No. 10 Arizona in Tucson. Already, not even halfway through the season, some fans, via social media, are demanding quick improvement.
USC Coach Steve Sarkisian brought Wilcox with him from Washington, where the former Oregon defensive back served as the Huskies' defensive coordinator for two seasons.
Despite the gargantuan yardage totals in the losses, Sarkisian is pleased with Wilcox's performance.
"He's doing a really good job," Sarkisian said this week, adding, "Justin is a great football coach and we're lucky to have him."
USC fans did not share those feelings last month after the Trojans failed to make effective adjustments during the 37-31 loss to Boston College.
The tension dissipated two weeks later when the defense did not give up a touchdown in a 35-10 victory over Oregon State. But whatever goodwill that accrued evaporated in the final four minutes against Arizona State.
"It's football — I understand that," Wilcox said of fans' reaction to the loss. "This is what you sign up for."
But he adds, "I think we're really close to playing pretty damn good."
Wilcox, 37, served as Boise State's and Tennessee's defensive coordinator before he replaced the fired Nick Holt — a former USC assistant — on Sarkisian's Washington staff in 2012.
Wilcox's coaching style differs from those of Kiffin or Pendergast, both of whom came to USC with NFL backgrounds.
Kiffin tinkered in his office late into the night and mainly stayed on the periphery of drills during practices. He occasionally erupted with emotion.
Pendergast, who also coached defensive backs, was a quiet presence and often appeared to let players shoulder responsibility for decisions on the field.
Wilcox is in constant motion during workouts, oversees several drills and is hands-on with players.
Junior cornerback Kevon Seymour said Wilcox was not to blame for the defense's struggles against Arizona State.
"It's not the coach's fault," he said, adding, "We have to make plays out there."
Wilcox's unit was not the first USC defense to turn in an embarrassing performance in recent seasons.
Kiffin's USC defenses experienced some legendary breakdowns, including in 2010 and 2012 against Oregon at the Coliseum.
Pendergast, who coached at California in 2010-2012, directed a 2013 Trojans defense that ranked first, statistically, in the Pac-12 Conference. But the Trojans did not play Oregon or Washington, the conference's top two offenses.
And Pendergast, like Wilcox, also struggled with the Trojans in a loss to Arizona State. USC gave up 612 yards in 62-41 rout at Tempe, Ariz., Lane Kiffin's final game as head coach.
In the next game, USC gave up 508 yards but held off Arizona for a 38-31 victory.
Wilcox and USC's defense on Saturday face an Arizona team that ranks seventh nationally in total offense. Redshirt freshman quarterback Anu Solomon has helped lead the Wildcats to a 5-0 record and No. 10 ranking in the Associated Press media poll.
USC's defense has enjoyed some bright spots. The Trojans rank fourth nationally in third-down conversion percentage. They are 24th in red-zone defense.
But the Trojans must deploy a better pass rush and be cognizant of the Wildcats read-option scheme. USC's eight sacks rank tied for 94th among 125 major college teams.
Senior linebacker Hayes Pullard said the Trojans must play a full game. "We've been playing some games, front end is killing, back end is struggling," he said, "Or back end is killing and front end is struggling.
"We've just got to play a full, complete [game]. Dominant pass and dominant run."
Wilcox anticipates that will occur.
"We've just got to do a better job as a whole, because when we put together a complete game, I think everybody's going to be saying, 'Wow, that's a pretty good defense,'" he said. "But we just haven't done that yet."