Finton Connolly is Arizona's only interior defensive linemen with any substantial Division I experience.

Key returneesFinton Connolly (6-5, 301, RS SR), Mykee Irving (6-3, 337, RS FR), Nahe Sulunga (6-2, 270, RS FR)

Key newcomersKane Bradford (6-5, 270, FR), Trevon Mason (6-5, 280, JR), Myles Tapusoa* (6-2, 326, JR)

(*-midyear enrollee)

The big question: Can anyone replace the production of PJ Johnson, who eschewed a sixth year of eligibility to enter the NFL draft?

It’s going to be a sizable challenge.

Johnson was among the Wildcats’ most pleasant surprises in 2018.

A transfer from City College of San Francisco, Johnson became a force in his one and only season in Tucson. Johnson’s 8.5 tackles for losses ranked second on the team. His three sacks tied for third. He also had two fumble recoveries, one forced fumble and a safety — all while missing two games.

Despite weighing well over 300 pounds, Johnson played defensive end at times. He even rushed from a two-point stance on occasion. He forced opposing offenses to account for him.

There’s no obvious candidate to fill that role. But it’s important to remember where things stood a year ago: No one knew how good Johnson would become.

His credentials were intriguing, to be sure. The fact that he ran with the ones from the start of spring camp suggests the coaches had some inkling of what he could do. But it’s not as if Johnson came to the UA as a can’t-miss pro prospect.

The only known quantity among the six players listed above is Connolly, who has proved he can be a productive rotation player at the very least. Everyone else is a mystery.

The newcomer whose profile most resembles Johnson’s is Tapusoa. He’s listed at 326 pounds. He’s slated to participate in spring ball. He was credited with 56 tackles, including 11.5 TFLs, in his sophomore year at Eastern Arizona College (which finished with the best record among all the Arizona JCs). That’s tremendous production, at any level, for an interior defensive lineman.

But you never know how it will translate to Division I. For every PJ Johnson there’s a Sione Taufahema, another 300-plus-pound JC transfer who never could stay healthy and never saw the field for the Wildcats.

Arizona is going to need at least two others, maybe three, to emerge alongside Connolly. Besides Johnson, the Wildcats also must replace sidekick Dereck Boles, who piled up 35 tackles, including five TFLs, two fumble recoveries and one forced fumble last season.

As with the offensive line, defensive line is a position where Arizona might look to add a player or two via the graduate-transfer market. The problem is, those are the hardest guys to find. One such candidate, Roe Wilkins of Rice, is headed to rival Arizona State.

Although Johnson put up numbers, the primary responsibility for the interior defenders in Marcel Yates’ scheme is to occupy blockers and keep the linebackers clean. The presence of Johnson and Boles helped Colin Schooler and Tony Fields II combine for more than 200 tackles.

But it sure is nice when the big guys can make plays too. Johnson has that ability. It’s rare.

The Wildcats unearthed one of those gems a year ago. Perhaps they can do so again.