Backup spin

McLeod Bethel-Thompson is just a headache away.

That’s how the line of succession at quarterback reads again this week for UCLA’s football team, as it prepares to play Oregon State on Saturday.

Ben Olson sat out Saturday’s game against Washington after suffering all week from lingering headaches. Patrick Cowan limped off with a partially torn knee ligament during the 44-31 victory over the Huskies. Olson has been cleared to play this week and went through practice Tuesday.

Meanwhile, walk-on Bethel-Thompson -- with a hospital-like name (Cowan underwent an MRI at Bethel Thompson Memorial?) and only POW-like info in the media guide (name, rank, serial number) -- is on call in case Olson has more headaches than he causes on the field.

“I don’t think it has really sunk it yet,” Bethel-Thompson said about being the Bruins’ backup quarterback. “I’m just trying to stay in the moment.”

Moments have a habit of arriving. Olson is expected to start, with a chance to exorcise his Utah ghosts -- three passes intercepted in a 44-6 loss to the Utes. But keeping quarterbacks healthy hasn’t been part of the Bruins’ game plan over the last year. Olson and Cowan have swapped places four times now.

Bethel-Thompson found that out a week ago when Cowan hobbled to the sideline with what is being called a partially torn medial collateral ligament in his right knee. Bethel-Thompson guided the Bruins, conservatively, through the last 13 minutes, with tailback Kahlil Bell throwing the only pass in that time.

“Getting out there and finding out it was the same game, that people out there are still players, they’re amazing, but you can play with them, was good,” said Bethel-Thompson, who also did mop-up duty against Stanford in the season opener.

This is scheduled to be a reboot for Olson, after glitches in his previous two starts against Brigham Young and Utah. He has not thrown a touchdown pass since the fourth quarter against Stanford in the season opener. His completion percentage (50.5%) is last among Pac-10 starting quarterbacks. And while it took a village to flop in Salt Lake City, Olson did his share.

By the end of that game, the Utes’ body of work on Olson’s body (five sacks) left him unable to play last week. UCLA officials refrained from calling it a concussion, saying only that Olson was suffering from lingering headaches and nausea.

“I didn’t start feeling better until Thursday night and Friday morning,” Olson said. “Then they put me through about a million tests, so I’m good to go.”

After a week off, Olson seems to have a lot to live up to after Saturday’s game.

Cowan stepped in, as he did last season when Olson suffered a knee injury, and made big plays, some out of chaotic moments, to nudge the Bruins’ offense out of neutral: UCLA had only one touchdown in the previous six quarters.

The Bruins won and were able to cleanse the pallet against Washington, but Olson was a spectator.

“You kind of have that bitter taste still in your mouth from your last game,” Olson said. “I’m looking forward to having the opportunity to go up to Oregon State and get rid of that taste. That’s the best way to get over a disappointing game, play again and get it out of your system.”

Olson and Bethel-Thompson took drastically different paths to get to Westwood.

Olson was the top recruit in the nation, considered a can’t-miss prospect. Bethel-Thompson was more a can’t-find one.

He was a latecomer to the game when he arrived at San Francisco Balboa High as a sophomore five years ago.

“This big, skinny kid came and to me and said he wanted to play quarterback,” Balboa Coach Keith Minor said. That might have been the end of the conversation, then Bethel-Thompson threw the pass.

“I was standing next to my brother and a football zipped across the field and it made a sound I hadn’t heard since I played college football,” Minor said. “There’s a certain sound you hear when a guy with a Division I arm throws the ball. I turned around and it was this skinny kid. I got a big grin on my face because I knew we had something special.”

Bethel-Thompson started as a sophomore and led Balboa to the city championship game as a junior. He threw for more than 2,000 yards and 19 touchdowns as a senior, yet few seemed to notice. Those that did didn’t seem to care.

Stanford passed. Idaho State lost interest.

“He’d go on trips and to camp and everybody would say there was something wrong with him, his feet or his arm,” Minor said. “It was all nonsense.”

UCLA Coach Karl Dorrell, though, said, “we felt he was a diamond in the rough,” and encouraged Bethel-Thompson, now 6 feet 4 and 222 pounds, to walk on.

“Since the day I walked in the door, he has sunk his teeth into this offense,” offensive coordinator Jay Norvell said. “He’s very bright, with a good arm and he picks up concepts quickly. Of course, he’s mad at me because I didn’t let him throw the ball Saturday. He hasn’t talked to me in three days.”

No worries. That moment has passed. Bethel-Thompson is awaiting the next one, which the Bruins hope doesn’t come this weekend.

“It was good to get out there and see the different defenses in the flesh instead of on tape,” Bethel-Thompson said. “But I will be happy to watch Ben play.”

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chris.foster@latimes.com