The only thing missing from USC’s spring game is the actual game

Michael Pittman’s laboratory is tucked in a corner of USC’s practice field. He retreated there, usually with two team managers, for about 30 minutes after every practice this spring.

A manager would load the ball into the passing machine. Clank. Pittman would pose as if he were reaching for a pass and — thump — watch the ball whiz into his hands.

He repeated it hundreds of times. Clank. Thump. He practiced one side, then turned around. He went high and low. Clank. Thump. Often, he was the last player left on the field.

Pittman and those like him, those not yet stars who are fighting for a handful of starting jobs, are used to toiling in obscurity.

Saturday’s spring game has turned into their showcase.

The exposure is more by necessity than by design: The one thing missing from USC’s spring game will be ... the spring game itself.

USC fans will still have to pay $10 to enter. They will still have to pay $15 if they want to park. But coach Clay Helton announced this week that the team is too banged up for a full scrimmage.

Helton ticked off a list of names he’d written on an index card after Thursday’s practice, “the couple guys,” he said, “that are going to be out.”

“Obviously Kenny Bigelow will be out. Isaiah Langley will be out,” he began.

Then, he added more than a couple: “Porter Gustin, Andrew Vorhees, Daniel Imatorbhebhe, Tyler Petite, Deontay Burnett, ‘Pie’ [Keyshawn] Young. As well as Chuma Edoga.”

At least four of the nine players are starters. Two additional starters, Toa Lobendahn and Viane Talamaivao, were already ruled out. Though none have injuries that will extend into the regular season, their absence means USC will again play what Helton called “basically a situational practice.”

The circumstances have left the receivers as the most intriguing position to watch Saturday. No position will be more tightly contested.

Quarterback Sam Darnold, a Heisman front-runner next season, will be the main attraction. But the two biggest unanswered questions entering fall camp are: Who’s protecting Darnold? And who, other than Burnett, will catch his passes?

Saturday won’t provide much clarity on the offensive line, but the receiving corps has developed with more promise. The Trojans have established depth. They just haven’t yet identified the player who will take over the position vacated by JuJu Smith-Schuster, the team’s No. 1 receiver for two seasons.

Pittman, a sophomore, was the most consistent in spring. He also flashed explosiveness: Last week, he fought through a penalty to haul in a touchdown in a simulated overtime period. The thousands of repetitions after practice were necessary. Pittman didn’t play receiver until he was a junior in high school — and even then, he wasn’t sold on the move.

“It probably took me up until my senior year that I actually thought I was going to be a college wideout,” he said.

The job isn’t Pittman’s yet. Tyler Vaughns had slumbered through a quiet redshirt season last year but awoke midway through the spring, when he made three highlight-reel receptions in one practice. Since then, Darnold said, Vaughns and Pittman “are going at it.”

Jalen Greene also took first-team repetitions. Pittman said all three could be needed. No single person, he suggested, would make up for Smith-Schuster.

“JuJu was the No. 1 receiver because he was the most productive, but there’s not a spot designated like he’s always going to get the ball,” Pittman said.

The defense, which outplayed the offense for much of the spring, was less turbulent. Eight starters returned from last season, and Jack Jones locked down the open cornerback job with what Helton called an “exceptional” end to spring practices.

Marlon Tuipulotu, an early enrollee, assumed the first-team defensive tackle position, but the role will be contested by Bigelow when Bigelow returns in full in the fall.

That left John Houston Jr. and Jordan Iosefa to wage the only true positional battle on the defense, at middle linebacker. Houston emerged to play with the first team, though he said, “I don’t think anything’s secure.”

Houston was arguably the best recruit in arguably the nation’s best recruiting class two years ago. But a back injury marred his first year, and he redshirted. Last season, he never threatened Michael Hutchings’ starting job, and he was marooned mostly on special teams.

He was determined not to waste more time this offseason. He vowed to use even his off time to get stronger. Roommate C.J. Pollard would challenge Houston to push-up contests at all hours.

“If we’re bored, playing Madden, sometimes we bet,” Houston said. Loser does 100.

Their Madden games are “back-and-forth,” Houston said. “But I give it to C.J. on that one.”

That’s OK with Houston: More Madden losses mean more push-ups.

Helton said Houston’s injury-riddled first year gave Houston perspective. Houston accepted his bit role last season without complaint “just for the joy of being out here practicing and playing again,” Helton said.

So Saturday — game or not — will matter at least to Houston, his chance, finally, at the spotlight.

zach.helfand@latimes.com

Follow Zach Helfand on Twitter @zhelfand