The injury puts the offense in the unproven hands of Kedon Slovis, an 18-year-old freshman. The prospect of that left Helton mulling whether to ask Jack Sears — a junior who played admirably in last season’s 38-35 loss to Arizona State in his only career start — to return after Sears entered the transfer portal last week as a reaction to dropping from second to fourth on the depth chart.

While it’s perhaps unfortunate that U.S.C. may be left with a greenhorn quarterback after transforming its offense to take advantage of Daniels’s arm and a strong receiver corps, it is also in keeping with how the Trojans under Helton have been a program defined by a lone player — their quarterback. When Sam Darnold was elevated to starter as a freshman, he took the team to a Rose Bowl win and a Pac-12 title in two seasons. When Helton has had anyone else at quarterback, the Trojans are 12-13.

More is expected at U.S.C.

But it is now 10 years since Pete Carroll returned to the N.F.L. The days of star-studded teams, a rollicking Coliseum crowd and the Trojans commanding a national stage seem like an epoch ago. The crowd on Saturday night, announced at 57,329, was the smallest home opener since Carroll’s first game, in 2001.

“Comeback mode,” Swann said last week, describing the state of the program in an interview in his office. “No one’s happy, certainly for any program with a 5-7 season, and certainly not here at U.S.C.”

Swann, who extended Helton’s contract through 2023 in advance of last season, said the players and coaches became too complacent last year. He brought in Tom Moore, Peyton Manning’s longtime offensive coordinator in Indianapolis, to evaluate the offense.

But Swann said he brought Helton back because there has been so much recent upheaval — the Trojans have had three head coaches and two interim coaches in the previous six years — and Helton, who had never been a head coach before being hired by the previous athletic director Pat Haden, needed time to grow.

“You’ve got to give people a chance to execute their game plan, get their people in and make it work,” Swann said. “That’s where we are with Clay. It would be great if you hired the coach, everything the coach needed was in place, and they won instantly and it took off. It doesn’t normally happen that way.”