USC’s defense credits Helton with successful, more aggressive approach

The USC football unit that opened the season as a major question mark is a big reason why the Trojans are riding a three-game winning streak entering Friday night’s game against Colorado at Folsom Field.

USC’s front seven has 13 sacks in the last four games, has pressured quarterbacks into seven passes for interceptions in the last three, and shut down one of the Pac-12 Conference’s top rushing attacks in last week’s victory over Arizona.

“Our hardest opponent this year has been ourselves,” linebacker Su’a Cravens said. “We had been missing tackles, jumping out of gaps and not knowing our assignments.

“Once we get that buckled down, which we have, you see what happened the last couple weeks.”

USC is surging under interim Coach Clay Helton, whose drive for the permanent position could ride on the outcome of the final three regular-season games.

The Trojans close with Oregon and UCLA, but first comes a Colorado team that has only one Pac-12 victory but several close losses.

The Buffaloes were tied with Oregon at halftime and trailed by only seven points early in the fourth quarter before the Ducks pulled away. Colorado led Arizona by seven points at halftime and into the fourth quarter. The Buffaloes defeated Oregon State before losing to UCLA, 35-31.

Colorado lost to Stanford, 42-10, last week.

“This is a different Colorado team than we’ve faced over the last couple years,” Helton said.

USC’s defensive line also has displayed a different, more aggressive look the last few games.

Against Arizona, senior nose tackle Antwaun Woods had three of the Trojans’ 10 tackles for loss, including two of six sacks.

“Someone gets a sack and it’s like, ‘Damn, I’ve got to get one too,’ ” defensive lineman Delvon Simmons said. “Now that they’re coming, we want to keep them coming.”

Asked to explain their improved play, multiple front-seven players pointed to Helton.

Just as he did before the 2013 Las Vegas Bowl, Helton has put an emphasis on having fun. He also has tweaked the practice routine and delegated many of his offensive responsibilities to assistants so that he can inject himself into defensive drills.

“I wanted them to feel my presence and feel my passion for them and try to help with the defensive front and offer any knowledge that I can,” Helton said, adding, “I just don’t think you can be on one side of the ball.”

Linebacker Scott Felix said Helton’s presence and emphasis carries over to games.

“It’s just different because Coach Helton is over there, personally,” Felix said. “He’s not watching you on film and critiquing you in the film room. He’s there motivating you and he just gives you positive reinforcement that makes you feel like you’re doing better. It makes you want to do better for him.”

Defensive lineman Claude Pelon, who made a key fourth-down stop against Arizona, said focus improved under Helton.

“Now we understand what we have to do and how the game is played,” he said. “It helps us have more production.”

Woods said there has been more emphasis on fundamentals and technique.

Helton praised defensive coordinator Justin Wilcox for the in-game adjustments he made against Arizona and said Wilcox would continue to handle defensive calls.

Helton described his team’s performance against Arizona as “the third week in a row of really buying into the physicality of playing big-time defense, stopping the run and getting to the quarterback.”

USC’s defense must continue to perform against Colorado before major tests against Oregon’s explosive offense and UCLA quarterback Josh Rosen.

That still might not be enough to win the Pac-12 South.

The Trojans, 6-3 overall and 4-2 in Pac-12 play, defeated Utah, but that remains the Utes’ only loss.

For USC to win the division, the Trojans must win out and Utah must lose one of its remaining games, against Arizona, UCLA and Colorado.

“We control our destiny if Utah loses,” Cravens said. “So all we’ve got to do is do our part — and hope Utah slips up.”

gary.klein@latimes.com

Twitter: @latimesklein