Listening to offensive line coach Bill O'Boyle after the team's April 17 spring practice, it's clear this season up front will be built on three things: competitive depth, a renewed sense of toughness and superlative left tackle Caleb Tiernan.

With a wave of experienced transfers and rising young players fighting for snaps across the line in spring ball, Tiernan stands alone as a stalwart, riding a 30-game streak of starts into the 2025 campaign.

"CT is the mainstay, man," O'Boyle said of the massive 6-foot-7, 329-pound veteran. "I talk all the time about wanting competition at each position with the offensive line, but he's been [an exception].

"What he's done from last year [at] this time until now, he's bought in... He shows up when I'm in the weight room at 5:15 in the morning, he's working."

Tiernan in years past has been characterized as a somewhat gentle giant off the field, keeping to himself and honing his craft. The spring of 2025 has seen him shift a gear from the best player on the line to its best leader.

"This group, these guys are dedicated like no other," O'Boyle said. "CT is one of those guys that wasn't real vocal last year, but he's been more vocal [this year]. He's on our leadership council, he's taken some huge strides."

Northwestern's left tackle has been a prestigious position since Rashawn Slater took the helm in 2019, passing the baton to Peter Skoronski in 2021. Both are now playing in the NFL.

Skoronski was back in Evanston for a practice on April 1, and the bond between past and present continues to grow.

"We spent some good years together and there's a lot of stuff where if I have questions, I can reach out to him," Tiernan said. "We're still friends, too, so I'll also send him something I see that's funny, or something happens with one of our teammates. It's been a positive relationship."

Heading into his fifth and final year in Evanston, it's Tiernan's turn to set the standard and mold a cohesive unit out of a fresh position group filled with experienced veterans in their fifth, sixth or even seventh year of college ball, as well as younger players looking to learn and challenge for reps of their own. This time last year, the Wildcats had seven players in the offensive line room in spring ball. Now, it's nearly tripled to 19.

"Our numbers are night and day," O'Boyle said. "I'm hoping we'll be around the 20 [player] mark when fall camp starts. That competition part is everything, we finally have guys stepping up, competing, making each other better."

O'Boyle thinks with Tiernan setting the standard, and veterans like Xavior Gray from Liberty, Evan Beerntsen from South Dakota State and center Jack Bailey back from injury, they can find a new edge up front.

"All that maturity really helps with the toughness part, not only mentally but physically," O'Boyle said. "We've made some strides there and we had to. This past fall, we were way too soft at times..."

Chemistry is the be-all, end-all for an offensive line, and Northwestern saw that last season, when a variety of injuries forced them into starting nine different players on the line in their 4-8 campaign.

Spring ball is a long ways away from the start of the season, but the Wildcats have had some early opportunities to build that bond taken away by the ever-nagging injury bug. Both Gray and Bailey have gone down with ankle injuries: Gray attends practices in sweats, Bailey in a boot.

But O'Boyle says not to worry, both players should be cleared to return by the end of May to start work in earnest on righting the ship up front.

"The main thing we say every day is fast and physical," Tiernan said. "I think last year we took a step back from that, whether we weren't focused or it was only in the back of our minds, we've really pushed this offseason to be fast and physical."

Part of that renewed effort will be new assistant Ryan Olson, the team's run-game specialist, who was brought in from his role as offensive coordinator/offensive line coach for South Dakota State by head coach David Braun and NU offensive coordinator Zach Lujan.

Braun said in an appearance on BTN that Olson could have followed SDSU head coach Jimmy Rogers to Washington State but instead opted for the Wildcats. It'll be up to him and O'Boyle to figure out a depth chart that is suddenly overcrowded.

"It'll play itself out," he said. "I've talked with Coach Olson about who's No. 1 at this spot or that spot, and I think with the rotation this spring, guys have pushed others. I'm not ready to just label a guy a starter. That's going to show itself over the summer."

With so much evaluation ahead, the new brain trust of O'Boyle and Olson can count on at least one thing: Tiernan will be starting at left tackle.

Editor's Note: At the time of publication, Northwestern listed 21 offensive linemen on their roster. The program has since updated Landon Lauter and Logan Uihlein's positions to defensive line, the story has been edited to reflect the number is now 19.