Perhaps it was the frustration of losing to Notre Dame for eight consecutive years.
Or, perhaps it was the frustration that quarterback Todd Marinovich endured last year as a redshirt freshman when he came ever so close to leading USC to a victory over the Irish at South Bend, only to lose, 28-24.
In any event, Marinovich believes that any chance USC had of beating Notre Dame Saturday night at the Coliseum was taken away by an official spotting the ball in the final minute of the game.
It was USC's last gasp when Marinovich passed to his favorite receiver, Gary Wellman, on fourth down and 11 from the Trojan 44-yard line.
Wellman had to come back for the ball. Then, he turned and tried to reach the first-down marker while being knocked out of bounds.
An official said he came up short by about a yard, and Notre Dame took possession, running out the clock in its 10-6 victory.
"I couldn't believe the last call," Marinovich said. "I expect to be homered in South Bend, but not at the Coliseum. It's disappointing to end on that note.
"I don't know where he (official) spotted it. It was just a bad spot. It was shocking."
Marinovich protested vehemently about the spot to an official and was assessed a dead-ball, noncontact penalty of 15 yards.
For USC at the time, it didn't matter. The game was virtually over.
Marinovich confirmed that the penalty was directed at him, saying, "Yes. It was well-deserved, too."
However, replays that Wellman was short of the first down as he was knocked out of bounds. He then tried to reach for the first down marker. "I thought I dove and put the ball over (the marker)," Wellman said. "The official didn't think so. He marked my body, but not the ball."
Then, Wellman added: "The whole thing was a blur. I thought I was far enough, but I guess I wasn't."
So in a series marked with controversial plays, such as Michael Harper's disputed touchdown in USC's last victory over Notre Dame at the Coliseum in 1982, this one doesn't apparently merit much recognition.
USC Coach Larry Smith said Wellman was held by a Notre Dame defender on the last pass play.
Wellman didn't agree, saying, "I don't remember anyone distinctly holding me."
Obviously, USC was frustrated while scoring only two field goals.
The game was in contrast to USC's 45-42 victory over UCLA a week ago Saturday when offense, not defense, was the theme.
After accepting the official invitation to the John Hancock Bowl Dec. 31 to play Michigan State in El Paso, Smith commented on the latest loss to Notre Dame.
"Any time you score only six points against Notre Dame, you don't have a very good chance of winning," said Smith, whose coaching record is 0-4 against the Irish while at USC.
"Our defense played well and our kicking game was good. We moved the ball offensively (302 total yards), but we didn't score. If you could point to any one thing, it would be dropped passes."
An example would be the third-down play preceding Marinovich's pass to Wellman. Fullback Scott Lockwood dropped Marinovich's pass at midfield.
"We had three, or four passes that went out of receivers' hands," Smith said. "Those were big plays.
"But we have nothing to be ashamed of. The bowl game is the best possible scenario for us."
USC linebacker Scott Ross, who has publicly expressed his loathing for Notre Dame, was proud of USC's defensive stand.
"We can hold our heads up high," Ross said of the defense. "I have no control over the offense, but I have a good say in defense and I thought we played well. Our goal each week is to hold the opposition to 10 points--and we all did that."
In the end, though, it was just another frustrating loss for the Trojans to their traditional rival.