Clay Helton

USC offensive coordinator and quarterbacks coach Clay Helton, shown at practice last season, guided USC to a Las Vegas Bowl victory over Fresno State in December as interim head coach before returning to his regular duties under new Coach Steve Sarkisian. (Luis Sinco / Los Angeles Times / April 5, 2014)

Four months ago, Clay Helton was drawing up a postseason game plan and overseeing USC's staff as interim coach of the Trojans.

He guided USC to a Las Vegas Bowl victory over Fresno State in December, and was subsequently rewarded when new Trojans Coach Steve Sarkisian retained him as offensive coordinator and quarterbacks coach.

Helton has spent the last four weeks installing the fast-paced, no-huddle offense that Sarkisian brought from Washington. The 41-year-old Helton had run a no-huddle system as Memphis' offensive coordinator before Lane Kiffin hired him at USC before the 2010 season.

Going back to an assistant, after serving as interim coach, has not been a problem.

"To be a part of this system again and to help in any role that I can is very satisfying, very rewarding," Helton said Saturday.

Helton and receivers coach Tee Martin are the only holdovers from last season's USC staff, which endured Kiffin's late-September firing and Ed Orgeron's abrupt departure after Athletic Director Pat Haden hired Sarkisian in December.

Sarkisian was impressed by the way Helton handled the tumult.

"That was a difficult situation — how it all went down when I got hired," Sarkisian said.

Helton's command and poise during practices and meetings while serving as interim coach also won over Sarkisian.

"I just thought to myself, 'How can I not have this guy on our staff?'" Sarkisian said.

Helton is one of two USC assistants who won games as interim coaches in 2013: tight ends coach Marques Tuiasosopo guided Washington to a victory in the Fight Hunger Bowl after Sarkisian was hired by USC.

Helton is overseeing an offense that has run more than 1,000 plays through nine practices.

Counting "walk-throughs" — which are essentially practices without footballs — Sarkisian said the team has run 2,000 plays.

"I'm just a believer in muscle memory," Sarkisian said, "of getting on the field and doing it over and over and over again."

Sarkisian does not discount the value of film study. But he said running and defending the plays, rather than watching them, allowed players to learn from mistakes.

"You can improve more rapidly," he said, "and retention is better."

The results, of course, won't be known until fall, when the Trojans begin a 12-game regular season that starts with an Aug. 30 opener against Fresno State at the Coliseum.

Scrimmage period

The Trojans went through a short scrimmage period with live tackling for the second time this spring.

Receiver Nelson Agholor adjusted during a deep route and caught a pass that completed a long touchdown play from quarterback Max Browne. Walk-on running back James Toland also scored a touchdown during an otherwise uneventful period.

Browne and junior quarterback Cody Kessler have completed about 70% of their passes during workouts, Helton said.

"If we can eliminate sacks and really get that ball out quickly, both are going to be very good quarterbacks," he said.

Helton also praised freshman Jalen Greene.

"I'm very excited about how fast he's picked up the concepts," he said, adding, "He has very good tools and will be a very promising quarterback here."

Quick hits

Players were not made available to the media after practice. More than a dozen players participated in a relay race during the annual Swim With Mike event that raises money for scholarships for physically challenged athletes…. The Trojans resume workouts Tuesday.

gary.klein@latimes.com

Twitter: @latimesklein