Biggest shoes to fill: USC

Starters in, starters out. That’s college football. Players’ eligibility expires, and they leave for the rest of their lives, whether that includes the NFL or not.

And they leave behind shoes of various sizes that need to be filled.

Our concern with this series? The biggest shoes -- in some cases Shaq-like size 23s.

Biggest shoes: Quarterback Matt Barkley

You could go a couple of ways with USC. Center will be a huge position battle, with potentially three players battling to replace Khaled Holmes. The No. 2 receiver battle is intriguing, as is spots in the secondary to replace Nickell Robey and T.J. McDonald. But four-year starters at quarterback are extremely rare. Barkley started 47 games for the Trojans -- more than any other USC quarterback in the school's history -- and went 34-13 as a starter. He leaves the program owning 20 school records and 10 Pac-12 records. While many agree that 2012 wasn't the season Barkley and the Trojans were hoping for, he still departs as one of the best statistical quarterbacks to ever play in the league and his charitable works were rewarded with the Wuerffel Trophy, which honors academics, athletics and service. He was a leader on and off the field and a player the Trojans will be hard-pressed to replace.

Stepping in: To be determined ...

Three players will compete to follow the guy who threw more touchdown passes than any other quarterback in the history of the league. When "USC" and "quarterback competition" come together, there is always intrigue. Max Wittek wasn't spectacular in his end-of-season audition -- losing to Notre Dame and then leading a floundering offense against Georgia Tech in the Sun Bowl. Cody Kessler has a couple of years in the system and was in a tight competition last spring with Wittek for the backup job. The X factor could be early enrollee Max Browne, a highly regarded pocket passer.