Even before being thumped by Notre Dame, the Stanford offensive line was struggling. Just why remains a mystery because, aside from the departure of guard David Bright, it’s the same group that tore open holes for Bryce Love and the rest of the offense a year ago.

This season, all the starters, including all three players who have been rotating at left guard, have been injured at some point. There has been a different starting lineup for each of the five games, so cohesiveness has been lacking.

Until Saturday night’s 38-17 drubbing, the line had been much better at pass blocking than run blocking. Then the Irish had five sacks — four of them by Jerry Tillery — and four quarterback hurries. The Cardinal also had major problems holding off the edge rushers.

Tillery has been inconsistent for much of his college career — he had a career best of just 4.5 sacks last year — but he’s considered the third-best senior defensive tackle in the country by NFLDraftScout.com. His draft stock rose considerably from this one game.

“This was our worst pass-protection game of the year,” Stanford head coach David Shaw said.

Stanford probably won’t face as good a defensive line the rest of the season. Guard Brandon Fanaika said Notre Dame’s line was the best he has faced as a college player: “They have some amazing talent.”

That said, there are likely to be many pass rushers and defensive fronts that will give the Cardinal problems unless the line dramatically improves. One such pass rusher is Utah’s Bradlee Anae, a quick 6-3, 254-pound junior who will put pressure on the Cardinal’s tackles in Saturday night’s game at Stanford Stadium.

“Up front, if you are not ready, they’re going to knock you back,” Shaw said of Utah, which rotates up to eight players on its defensive line. “They’re physical, they’re strong. … They’re big inside, as they always are. They’re tough to move, tough to uproot.”

One of the O-line’s problems is simply a lack of depth. Right tackle A.T. Hall, still not completely healthy, had to play the whole game against Notre Dame because, as Shaw said, “We didn’t have the luxury this week to rest him a little bit.”

Besides struggling with the outside pass rush, Hall had two holding penalties, one of which was declined, and a false start. Walker Little didn’t fare much better on the left side. He whiffed on Julian Okwara in the third quarter, allowing a quarterback hurry that just missed leading to an interception and on the next series, Little surrendered a sack to Khalid Kareem.

In the fourth quarter, Tillery had three sacks, beating, in order, guard Nate Herbig, Little and guard Devery Hamilton.

A former NFL scout who didn’t want to be identified because of his ties to the Stanford program, called the O-line’s performance against Notre Dame “a train wreck.”

He said he thought there were several problems.

“First of all, the guys are not strong,” he said. “None of those guys up front play with any kind of strength. Tillery ran over them. They couldn’t even slow him down and tackle him.

“They can’t anchor. I feel bad for (quarterback K.J. Costello). He couldn’t step up; it just was not pretty. They’re technique-poor. Their footwork is very inconsistent. I thought a lot of the guys have balance problems. You can’t be on the ground; Herbig was on the ground a lot. The two tackles over-set, so the defensive player could come underneath them and get a clean shot at the quarterback.”

Notre Dame was getting loads of pressure without blitzing, he noted. “When you can do that with a four-man pass rush, you’re dropping seven into coverage. Costello didn’t have a chance to find any holes. You tell me five guys can’t block four? That’s how bad that offensive line is.”

Shaw and the linemen steadfastly have defended first-year O-line coach Kevin Carberry, who previously worked for two NFL teams.

“It’s great to have the technique and the wisdom that he brings,” Fanaika said. “He’s been around some amazing talent. He definitely knows his stuff.”

Tom FitzGerald is a San Francisco Chronicle staff writer. Email: tfitzgerald@sfchronicle.com Twitter: @tomgfitzgerald