At the end of each practice, USC running backs huddle on the field for a short meeting.
They depart chanting, "R-B-U-U-U-U," the last few letters trailing off in a bass-and-baritone coda of group pride and strength.
But with junior Javorius Allen contemplating a jump to the NFL after Saturday's Holiday Bowl game against Nebraska, the strength and depth of USC's running back corps in 2015 is a major question mark.
If Allen decides to forgo his final season of eligibility and make himself available for the 2015 draft, sophomore Justin Davis and junior Tre Madden will be the only returning scholarship tailbacks.
"Our numbers are really quite low," Coach Steve Sarkisian said.
The lack of depth is a stark contrast to the 2007 season, when former Coach Pete Carroll began training camp with 10 scholarship tailbacks on the roster. Several were injured or recovering from injuries, but the Trojans never lacked for options.
"I always remember Pete saying, 'You can never have enough tailbacks, because you just don't know…,' " said Sarkisian, the offensive coordinator for that team.
In the years since, USC's tailback depth has shrunk because of injuries, transfers and NCAA sanctions that limited Trojans' recruiting classes to no more than 15 players, 10 fewer than the allowable maximum.
"It's one of the positions the sanctions probably hit the hardest," Sarkisian said.
Greg Biggins, national recruiting analyst for Fox Sports and Scout, said sanctions did not stop the Trojans from landing "upper echelon" running backs.
"But for added depth, having 10 less spots hurt," he said.
In 2010, before the sanctions were announced, USC signed a 17-player class that included tailbacks Dillon Baxter and D.J. Morgan and fullback Soma Vainuku.
In 2011, the scholarship penalty was stayed while USC awaited a ruling on its appeal of sanctions. That enabled former Coach Lane Kiffin and his staff to bring in 30 players, including eight who enrolled in January (and counted against the 2010 class) and 22 that signed in February. Allen, Amir Carlisle and fullback Charles Burks were part of the class. So was Madden, though he was recruited as a linebacker and played the position as a freshman.
In 2012, fullback Jahleel Pinner enrolled as a freshman, and Silas Redd transferred to USC from Penn State.
The 2013 class included Davis and Ty Isaac. The 2014 class was devoid of running backs.
In the last four years, USC also has experienced tailback attrition: Baxter was removed from the program, Morgan suffered several knee injuries, Carlisle transferred to Notre Dame and Isaac transferred to Michigan.
But going into training camp this season, USC appeared to have adequate tailback depth.
Allen was coming off a 2013 season in which he emerged as the team's most valuable player. Madden, who rushed for more than 100 yards four times in the first five games last season, appeared recovered from a hamstring injury that slowed or sidelined him the last eight games. And Davis was ready to show he was back from a season-ending ankle surgery.
But Madden suffered a toe injury early in training camp and has not played this season.
USC got through with the durable Allen, Davis and walk-on James Toland IV.
Allen, who has rushed for 1,337 yards and nine touchdowns, "was a warrior for allowing that to happen," Sarkisian said.
Davis, who overcame early fumbling problems to rush for 550 yards and four touchdowns, said Allen "has really played the mentor role for me."
Next season, Davis will be the elder for a tailback corps that Sarkisian aims to fortify through recruiting.
Dominic Davis, a running back/receiver from Mission Hills Alemany High, and Aca'Cedric Ware of Cedar Hill (Texas) have made verbal commitments to the Trojans.
USC also is pursuing Ronald Jones of McKinney (Texas) North High.
High school and junior college players can sign national letters of intent on Feb. 4.
"That is one position where I don't know if I can take a developmental guy," Sarkisian said. "I need some ready-made guys to come in and play."