Parker Zellers spent part of Tuesday “doing stadiums” — i.e., running up the steps at Arizona Stadium. Never mind that he has only four games left in his college football career, or that the team practiced earlier in the day. Zellers didn’t ascend from walk-on to rotation regular for the Arizona Wildcats by sitting out on his couch.

Anyway, when he would reach the top, the senior defensive tackle would take a moment to soak it all in.

“I was up there trying to remember all the good times, all the bad times, all the hard times,” Zellers said, “and how it’s made me a better person, a stronger person.”

These are mostly definitely the good times. Arizona is bowl eligible and sitting on the fringe of the top 25 entering Saturday’s home finale vs. Oregon State — Senior Night for Zellers and his classmates. A program whose future felt bleak a year ago now seems undeniably bright.

But to keep things going in a positive direction, the defensive front must up its game. The pass rush has eroded lately. The run defense withered last week at USC.

The Wildcats probably can get away with it against the underdog Beavers, who have only one win. That might not be the case on the road against Oregon and Arizona State.

It starts, as it always does, with the men burrowed into the trenches. Zellers and fellow senior Luca Bruno need to lead the way. Rich Rodriguez couldn’t think of two better candidates.

“Their attitude is as good as it could be,” said Rodriguez, who summed it up as follows: “Selfless. Work hard. ‘What do you need, Coach?’”

Arizona needs them to reveal their resilient sides one last time. While others pan the Wildcats’ defense for its bend-but-don’t-break tendencies, defensive line coach Vince Amey views that as a strength.

“Because they could easily give up and give in,” he said. “But they don’t.”

Zellers and Bruno embody that mentality.

Zellers wasn’t just any walk-on when he arrived at Arizona from Scottsdale Notre Dame Prep in 2013. He was a 6-foot-1-inch, sub-250-pound nose guard vying for playing time in the Pac-12.

“The first year I’d always question myself,” Zellers said. “But then once I got my opportunity, I realized I could make this happen.”

Coaches first started to take notice of Zellers on the scout team. The following year, when injuries and other issues struck, they turned to the undersized walk-on. He started six games for the 2014 Wildcats, who finished 10-4, totaling 20 tackles and a fumble recovery. Zellers has been a fixture up front ever since.

“He had that drive that he was going to be a starter,” Bruno said. “He’s undersized, underweight. That kid just has resiliency. He loves this game. You can see that out on the field.”

Bruno loves it too. If he didn’t, he might have walked away.

Bruno suffered a bad foot injury — a torn arch — late in the 2015 season. He came back last year but was never quite right. His tackles total fell from 29 to 12. He didn’t record a sack.

“I had a time last year where I was a little iffy about even playing,” Bruno said. “It healed for a good couple months in the offseason, but not really. Then I came back last year, and it wasn’t so great. It scared me. There were a couple times I thought this would be over. It was that bad.”

Bruno had some heartfelt conversations with Amey, whose words reassured him. Amey wanted to make sure Bruno wouldn’t leave the game with any regrets. If Bruno needed him at any point, Amey would be there.

“I’m happy we had that talk,” Bruno said. “It brought me to now, and I’m having one of the best years I’ve had.”

Bruno has 19 tackles in eight games. The Oak Park, California product sacked Sam Darnold at the L.A. Memorial Coliseum last Saturday.

That was a rare defensive highlight in a game in which Arizona surrendered 49 points and more than 600 yards — the latter happening for the second straight week.

At times like these, it’s important to have perspective.

Yes, the Wildcats’ defense has struggled the past two games. But it has improved in innumerable ways from last season, despite — or thanks to — the starting unit featuring multiple freshmen.

As fifth-year seniors who have endured plenty of ups and downs, Bruno and Zellers have a perspective many of their younger teammates lack. Zellers feels as if he has “seen it all” in his time at Arizona.

“I’ve been on an average team, I’ve been on a good team, I’ve been on last year’s team,” Zellers said. “I feel like I’ve seen different aspects, how (good) you can be and how bad a year someone could have.

“I wouldn’t say it’s easy to deal with, but easier than in the past. I feel like every good and bad thing that happens to you makes you stronger – makes you more prepared for whatever is to come.”

Zellers repeatedly mentioned how “thankful” he is to be in this position — bowl-bound no matter what happens over the final three games. Last year’s seniors didn’t get to experience that. They won their final game, against ASU, but it didn’t erase the pain of a 3-9 season.

These Wildcats, young and old, envision continued success. Khalil Tate and the offense have brought them this far. It’s time for the veterans on defense to take them the rest of the way.

“We want to go out with a bang,” Bruno said, “and I think everybody knows we’re going to go out with a bang.”