You didn’t need a PHD in football schematics to decipher the biggest problem with the Arizona Wildcats’ offense last season.

The line was a mess.

For reasons that remain muddled — Wonky pandemic season? Josh McCauley’s preseason knee injury? Guys playing in the wrong spots? — the line regressed in 2020.

Arizona allowed the most sacks (18) in the Pac-12 despite playing only five games. The Wildcats also lost the most yards on sacks (118).

On a per-game basis, those numbers rose significantly from 2019. Arizona allowed 2.8 sacks per game that year, 3.6 last year. Yardage lost climbed from 15.9 to 23.6.

With their quarterbacks regularly under siege, the Wildcats’ overall offensive output plummeted. Arizona fell from third in total offense in the Pac-12 (440.1 yards per game) to 11th (369.4) — and from seventh in scoring (26.9 points per game) to last (17.4).

Considering that Arizona’s sack-adjusted rushing average was virtually the same — 5.5 yards per attempt in 2019, 5.4 last season — the issues mainly can be traced to pass protection.

That’s where Brennan Carroll comes in.

Jedd Fisch selected Carroll to help coordinate Arizona’s offense and to coach its offensive line. Carroll never has been a full-time line coach, but he has apprenticed under some of the best, including Tom Cable and Mike Solari.

Besides quarterback, no position group carries more intrigue into 2021 than the offensive line. No games will be won or lost during spring practice, which starts Tuesday afternoon, but that’s when the foundation must be set. We explore that idea in the latest of our series of pressing questions about the Wildcats heading into spring ball:

How critical is it for Arizona to establish a cohesive offensive line during spring practice?

It’s paramount. It’s everything.

Fisch’s scheme won’t work if the offensive line doesn’t function at a high level. Whoever the quarterback is will struggle if he doesn’t have time to throw. The Wildcats’ promising batch of skill players won’t thrive if they don’t have room to operate.

Carroll inherits a group that’s largely unchanged from last season — for better or worse. Given that the line was largely unchanged going into last season, it’s hard to make that determination.

Spring additions include freshman center-guard JT Hand and veteran tackle Edgar Burrola, who’s back after being suspended last season. Fisch and his staff have not mined the NCAA transfer portal for offensive linemen. So growth will stem more from coaching and schematic changes than a personnel overhaul.

One player who won’t be part of the team in spring is Davis DiVall. DiVall, a transfer from Baylor, was announced in December as part of Arizona’s 2021 signing class. But DiVall encountered an academic issue that made him ineligible to enroll in January.

DiVall, who’s from Scottsdale, had no prior relationships with the current UA staff. As his family tried to navigate the eligibility issues, DiVall got lost in the shuffle.

DiVall is currently taking UA-approved classes at Scottsdale Community College and is on track to be eligible later this spring. It’s possible he could end up at Arizona later this year. The Wildcats have one more scholarship available for 2021.

Carroll undoubtedly will shuffle the deck and try different combinations in spring. He isn’t averse to playing more than five linemen and said he even prefers it.

We don’t know exactly what Fisch’s offense will look like. But we do know the quarterback will be under center at times, setting up the possibility of play-action passes.

That’s one way to help an offensive line. Another is incorporating tight ends as blockers and receivers. Fisch plans to do that too.

Carroll is an advocate of the “wide zone” blocking scheme. Zone blocking in general can have a whole-greater-than-the-sum-of-its-parts effect that should serve Arizona well.

“We’re always gonna keep it really simple to start with,” Carroll said. “We’re going to push them as far as we can in terms of learning — and then pull back if it goes too far.

“But it’s going to start real basic, real simple, so our guys can execute early on. We don’t want to have to say, ‘Three years into the program, they’ll be ready to go.’ We need to be able to win and compete right now, so that’s our goal.”