For USC’s defense, the takeaway from this game is positive

Arizona quarterback Khalil Tate flitted into the secondary with a head of steam in the second quarter against USC. This was exactly what the Trojans didn’t want to see: a mobile quarterback 23 yards downfield, heading toward safety Chris Hawkins.

“I knew from earlier in the game, he wasn’t trying to shake DBs,” Hawkins said. “He was trying to run us over.”

Hawkins braced himself, got low and launched. His helmet found the ball. The ball squirted loose, and Adoree’ Jackson picked it up and returned the fumble to Arizona’s 10-yard line.

It was one of four turnovers USC forced during the game. Iman Marshall was gifted an interception when Tate threw a pass right to him. Connor Murphy fell on a Zach Green fumble. And Ajene Harris ended Arizona’s offensive day by intercepting a pass late.

Those were enough to lift USC’s season turnover differential into the positives. USC had a negative-three margin entering the game, 11th in the Pac-12.

The takeaways are the latest development for a USC defense that improved markedly once it escaped a brutal opening four games. In the previous two games, USC had held Arizona State and Colorado to fewer than 100 yards rushing. The secondary had tightened, too. On Saturday, it allowed just 142 yards passing.

During the previous week of practice, multiple USC defenders said, defensive coordinator Clancy Pendergast had emphasized turnovers.

“It seemed like offensively, we were getting unbelievable field position,” USC Coach Clay Helton said. “I have to credit our defense.”

Smith-Schuster recovers

JuJu Smith-Schuster stretched for a high pass along the sideline in the third quarter Saturday. The ball whooshed above his hands. A cornerback careened into his lower back.

Smith-Schuster said his back had been bothering him for much of the season. The defender, he said, “hit the exact same right spot.”

Smith-Schuster crumpled to the turf, where he stayed for several minutes.

“It locked up, and I couldn’t move,” Smith-Schuster said. “For a good about two minutes, I was stiff and I had trouble breathing. I felt like I had the wind knocked out of me.”

Two teammates helped Smith-Schuster to the bench. He moved stiffly, then walked to the locker room.

X-rays revealed no fractures, and he soon returned to the sideline, although his day was done.

Moving more easily after the game, Smith-Schuster said that he was not seriously injured. Had the game been closer, he said, he might have been able to return for a few plays.

USC’s bye week gives Smith-Schuster extra recovery time, and he said he would be back for USC’s Oct. 27 game against California.

“I’ll be fine,” he said. “I mean, if I can break a bone and come back the following week, I feel like back spasms won’t be any problem.”

Mitchell injured

The outlook was more ominous for receiver Steven Mitchell, who planted his left leg during a punt return and collapsed to the turf without being contacted. He immediately gripped his knee.

1/18

USC receiver JuJu Smith-Schuster (9) celebrates with Darreus Rogers after scoring a touchdown against Arizona during the second half of a game on Oct. 15.

  (Rick Scuteri / Associated Press)

2/18

USC running back Ronald Jones II (25) crashes into the end zone for a touchdown during the first half of a game against Arizona on Oct. 15.

  (Rick Scuteri / Associated Press)

3/18

USC quarterback Sam Darnold scrambles for yardage during the first half of the game against Arizona on Oct. 15.  (Rick Scuteri / Associated Press)

4/18

USC defensive back Adoree’ Jackson heads upfield after recovering a fumble against Arizona on Oct. 15.  (Rick Scuteri / Associated Press)

5/18

Arizona tight end Matt Morin (15) plays quarterback during the second half of a game against USC on Oct. 15.

  (Rick Scuteri / Associated Press)

6/18

Arizona running back Zach Green carries the ball during the second half of a game against USC on Oct. 15.

  (Rick Scuteri / Associated Press)

7/18

Arizona quarterback Khalil Tate is pressured by USC defensive end Porter Gustin during the first half of a game on Oct. 15.

  (Rick Scuteri / Associated Press)

8/18

Arizona quarterback Khalil Tate is taken down by USC defensive end Porter Gustin during the first half of a game on Oct. 15.

  (Rick Scuteri / Associated Press)

9/18

USC running back Ronald Jones II (25) runs for a first down during the first half of a game against Arizona on Oct. 15.

  (Rick Scuteri / Associated Press)

10/18

Arizona running back Nick Wilson stiff arms USC defensive back Marvell Tell III (7) during the first half of a game on Oct. 15.

  (Rick Scuteri / Associated Press)

11/18

Arizona receiver Trey Griffey can’t haul in a pass while being defended by USC defensive back Iman Marshall during the first quarter of a game on Oct. 15.

  (Chris Coduto / Getty Images)

12/18

Tight end Daniel Imatorbhebhe celebrates his touchdown with receiver Deontay Burnett during the second quarter of a game on Oct. 15.

  (Chris Coduto / Getty Images)

13/18

USC running back Aca’Cedric Ware finds running room against Arizona on Saturday.  (Chris Coduto / Getty Images)

14/18

USC quarterback Sam Darnold throws a pass during the second quarter of a game against Arizona on Oct. 15.

  (Chris Coduto / Getty Images)

15/18

USC receiver Darreus Rogers is hit by Arizona safety Demetrius Flannigan-Fowles (6) and cornerback Jace Whittaker (17) during the first quarter of a game on Oct. 15.

  (Chris Coduto / Getty Images)

16/18

USC quarterback Sam Darnold throws downfield during the first half against Arizona on Oct. 15.  (Rick Scuteri / Associated Press)

17/18

USC Coach Clay Helton talks to an official during the first half of a game against Arizona on Oct. 15.

  (Rick Scuteri / Associated Press)

18/18

Arizona Coach Rich Rodriguez reacts on the sideline during a game against USC on Oct. 15.

  (Chris Coduto / Getty Images)

He left the game and walked to the bus afterward with his knee in a bulky brace. Helton said Mitchell would have an MRI exam on Sunday.

Boermeester’s boot

Aside from extra points and kickoffs, Matt Boermeester had a quiet afternoon. He was called upon just once for a field-goal attempt — from 54 yards away.

Boermeester displayed a powerful leg. The ball soared well above the crossbar, about halfway up the goalposts, with plenty of distance left. But it clanged off the right post.

Quick hits

Outside the visitors’ locker room at Arizona Stadium is a sign written in urgent font: “WARNING EXCESSIVE HEAT.” Saturday was the Wildcats’ first day game of the season — they avoid such games early in the season to stay out of Tucson’s scorching temperatures. By game time Saturday, the public-address announcer said the temperature on the field, where heat is amplified by the artificial turf, was 137 degrees. … Safety Leon McQuay III left the game with minor groin and hip flexor injuries.

zach.helfand@latimes.com

Follow Zach Helfand on Twitter @zhelfand