No position group at USC entered the spring surrounded by more uncertainty than the offensive line. With the key losses of Marcus Martin, Kevin Graf, John Martinez and Abe Markowitz, a new position coach in Tim Drevno, and the offense transitioning into Steve Sarkisian’s up-tempo, shotgun-based attack, no one knew quite what to expect. While there was certainly plenty of good to take away from their performance this spring, this is still a unit with more than a few question marks.

Both guard spots open

With only eight healthy scholarship players available, it was hard to ever get a real solid read on the offensive line, and as Sarkisian recently noted, this is a unit that will need to be solidified in the coming months.

That’s particularly the case at the guard positions, where, during spring drills, the Trojans featured a starting duo of early-entrant freshman Toa Lobendahn at left guard and second-year freshman Khaliel Rodgers at right guard.

And while both players – particularly Lobendahn -- showed promise, the entire competition at those spots is set to change dramatically as the Trojans gain an influx of talent from incoming freshmen as well as players returning from injury.

Of those players on the mend, senior Aundrey Walker, who is returning from a broken ankle, will be watched with particular interest. Establishing himself as a reliable starter at right guard in 2013 after an up-and-down 2012 campaign at tackle, he possesses veteran experience that could be invaluable to this unit.

Jordan Simmons, returning from a torn ACL, is a big mauler who was really starting to stand out in practice prior to his injury in the fall, and he’s another player who could make a run at a starting job on the interior.

Of course, in the case of both Walker and Simmons, it’s how their recovery goes, and what kind of shape they come back in -- particularly with the conditioning required for the new offense -- that will likely play the biggest role in determining whether or not they’re able to jump in and perform at a high level when fall camp opens up.

And then there is fifth-year senior Giovanni Di Poalo, as well as a pair of incoming freshmen guard candidates -- Damien Mama and Viane Talamaivao. Both youngsters arrive not only with more than their fair share of accolades, but also with unique talent and tremendous size -- giving them the look of potential instant impact performers.

Center of attention

With Martin off to the NFL, one of the new staff’s biggest priorities heading into spring practice was to find a capable starter at center. Max Tuerk, a tried and tested veteran who started 13 games at left guard in 2013, and the majority of the prior season at left tackle, wound up getting the call. While he did have some occasional difficulties in the snapping department, he performed solidly for the most part.

Still, while Sarkisian lauded Tuerk’s overall ability during the recent Pac-12 football coaches teleconference, he also appeared to leave the door open for competition through fall camp, so this isn’t over just yet. Both Di Poalo and Lobendahn lined up at the position in the spring, and have continued to do so this summer during the team’s volunteer workouts. Talamaivao is another key name to watch here, as he too, has been taking reps at this spot over the course of the last week. It will also be interesting to see if Mama gets a look here when he arrives on campus.

If Sarkisian and Co. did decide to go with someone other than Tuerk here, it’s a virtual certainty that the junior would still line up as a starter somewhere else. Arguably the Trojans’ sturdiest pound-for-pound offensive lineman, he could conceivably slide back over to left guard or either of the tackle spots without a hitch.

Stability at tackle

While the interior of the line still isn’t totally set, the Trojans do appear to be in better shape at both of the tackle spots -- at least when it comes to the starters.

No player drew more praise from Sarkisian following spring drills than third-year sophomore left tackle Chad Wheeler. Having started every game last season, he looks primed for a fantastic 2014 campaign.

Over on the right side, the emergence of Zach Banner -- who sat out most of last season after having hip surgery -- was one of the great revelations of the spring. Performing at the highest level of his career, the 6-foot-9, 345-pounder took over with the No. 1 group in place of Nathan Guertler midway through camp and never looked back. Considering the fact that he said that he wasn’t even quite back to 100 percent during those workouts, there’s reason to believe he’s only going to get better, and it will be interesting to see just how much farther he can continue to progress this offseason.

Still, Drevno needs to find out who else he can count on to contribute at tackle, if nothing else, to provide depth. Early entrant freshman Jordan Austin and Guertler were the primary backups in the spring, and then there’s also Nico Falah -- returning from a back injury. Highly touted incoming freshman Chris Brown has also been taking reps at right tackle during summer drills.