Stewart will test the defense

The numbers stand out.

UCLA gave up 557 yards rushing through the first seven games. The Bruins have given up 554 yards in the three games since.

They face a running back Saturday who is capable of gaining yards in short chunks or all at once.

Oregon’s Jonathan Stewart leads the Pacific 10 Conference with 1,273 yards rushing. His presence has become even more vital to the Ducks, as quarterback Dennis Dixon, a leading Heisman Trophy candidate, went out because of a knee injury against Arizona on Nov. 15.

“Trust me, this guy, we’ve been meeting our [butts] off to make sure we take care of this run game,” Bruins defensive coordinator DeWayne Walker said. “We’re still in the top 20 against the rush [nationally], not that stats mean anything. Have we been great? Naw. Have we been pretty good? Yeah. But we’ve got to be great this week.”

In their last three games, the Bruins gave up 274 yards rushing against Washington State, 128 against Arizona and 152 against Arizona State. In each of those three games, a back has broken free on a long touchdown run.

Arizona’s Nicolas Grigsby went 60 yards, getting a block from UCLA safety Chris Horton, who collided with teammate Alterraun Verner. Arizona State’s Keegan Herring went 71 yards, spinning outside after being stood up at the line of scrimmage.

“In the Arizona State game, it was, ‘I’m a lucky dude sometimes,’ ” Walker said. “We hit, we just didn’t finish the play. The Arizona game was the same. We had to adjust and didn’t have guys in place to make the tackle.

“I know you can’t, but if you take those two runs away, we give up 50-60 yards rushing like we normally do.”

The Bruins are 17th against the run nationally, giving up 111.1 yards a game. Yet, they had been yielding 79.6 a game until the Washington State game, when Dwight Tardy torched them for a 51-yard touchdown run.

The longest touchdown run against UCLA last season was Lorenzo Booker’s 25-yard run in the Emerald Bowl for Florida State.

“Each play is like a game,” Bruins cornerback Trey Brown said. “One play can make or break the game or your season. You’ve got to be able to know that. When they want to run the ball, we have to stuff it every time.

“You can be perfect nine out of 10 times, but that one time could be the play that hurts you. We just have to play for perfection.”

If healthy, Stewart could take the pressure off Brady Leaf, who will be filling in for Dixon. Stewart sat out practice part of this week with what is believed to be shoulder and toe injuries.

The Bruins know his abilities well. Stewart was the only back to gain more than 100 yards against UCLA last season. He had 121 yards in a 30-20 Ducks victory. The Bruins have had five opposing running backs go over 100 yards this season.

Ben Olson will be the Bruins’ backup quarterback Saturday, Coach Karl Dorrell finally said Thursday.

Olson, who was the Bruins’ No. 1 quarterback at the start of the season, has been out since suffering a torn ligament in his left knee against Notre Dame on Oct. 6.

“He’s excited about being part of a plan for this week,” Dorrell said.

Osaar Rasshan will start at quarterback. Asked about Olson’s availability, Dorrell said, “if needed.” Asked what the case would be for Olson to be needed, Dorrell said, “if needed.”

Dorrell added, “We’ll see where his head is at. . . . As the week progressed, he has looked better and better each day. He’s not going to have to feel perfect to play, he realizes that.”

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chris.foster@latimes.com

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UP NEXT

vs. Oregon (8-2, 5-2)

Saturday, the Rose Bowl

12:30 p.m., Channel 7