Much of what Purdue wants to do this season centers around the offense: Rondale Moore and David Bell, trick plays and scoring points.

But defense matters. And for Purdue, that brings a lot of questions heading into Saturday’s opener at home against Iowa (2:30 p.m. Central, BTN). The Boilermakers are transitioning into a new era, with co-coordinator Bob Diaco — he shares the DC duties with safeties coach Anthony Poindexter — installing his 3-4 front, a big change from Nick Holt’s more traditional 4-3.

Every defense, regardless of scheme, has basic tenets: stop the run, be good on third down, create turnovers. But let’s go deeper into Diaco’s D, taking a look at 5 goals for this season.

1. Feature budding star George Karlaftis

As a freshman last season, George Karlaftis burst onto the scene with 8.5 sacks, making him Purdue’s most prolific pass-rusher since Ryan Kerrigan nearly a decade earlier. He quickly became Purdue’s best defensive player, and it wasn’t even close. But much has changed for Karlaftis in the last year. Now, he’s playing end as part of a 3-man front — Diaco says the front will be multiple, with as many 4-man looks as 3 — and that will bring adjustments. Can Karlaftis get after the quarterback as frequently? Or will he be swallowed up by multiple double-teams? Diaco is charged with making sure it’s the former more frequently than the later. Purdue can’t let the 6-4, 270-pounder get lost in the new scheme.

2. Settle on a Dog

Purdue will go with 4 linebackers as part of its new-look defensive front. The big question during the offseason was simply … who? The Boilermakers don’t have an overwhelming abundance of experienced linebackers, with the only known commodity being inside linebacker Derrick Barnes, although the senior played defensive end — and very successfully — last season. But for Diaco’s defense to click, he’s got to find himself a couple of quality outside linebackers.

At “Cat” (the boundary outside ‘backer), he’s likely to slide in transfer DaMarcus Mitchell, a big 6-3, 270-pounder who can move down to put his hand in the dirt on the line on occasion. But the field linebacker — Diaco titles that the “Dog” — is a bigger question. Potentially it’s sophomore Jalen Graham, who made 8 starts last season splitting time between safety and nickel back. Or it could be UConn grad transfer Tyler Coyle, who led the Huskies in tackles as a safety last season. Whoever wins the job, it’s a critical one, playing in space — that might feel normal for the 215-pound safeties — but also playing in the box, trying to slow the run and blitzing the quarterback. It’s a big task.

3. Allow fewer big plays

If there’s one glaring reason why Jeff Brohm dismissed Holt and replaced him with Diaco, it might be the Boilermakers’ tendency to give up the big play. And it didn’t matter whether that was in the run game or pass, Purdue too often couldn’t stop it.

If the Boilermaker defense, one that finished 11th in the Big Ten in yardage allowed (428.8) last year, is to make a big leap, it’ll need to cut down on the chunk plays. It could. And if it does, the rebuilt secondary will have a lot to do with it.

During the offseason, Purdue brought in a few transfers to help solve the problem: Coyle, JC cornerback Geovonte Howard and Iowa corner D.J. Johnson. Howard or Johnson, or perhaps both, might jump in as a starters right away, with Johnson having received an immediate eligibility waiver this month from the NCAA and Big Ten. At the least, the two give the Boilermakers’ corner depth, to go along with former starters Dedrick Mackey and Cory Trice.

But where Purdue really needs upgrades is at safety, whether that’s veterans Brennan Thieneman or Simeon Smiley or promising youngsters like Cam Allen and Marvin Grant, a former 4-star DB by 247Sports who missed last season with an injury. Regardless of who, Purdue needs production.

4. Understand the scheme

Purdue wanted to spend its 15 spring practices installing Diaco’s new scheme, a big undertaking considering the significant differences from the primary 4-man fronts run by Holt. But the spring was cut in half by the COVID-19 outbreak, stymying the massive defensive install. And the fall hasn’t been smooth either, with the initial August start temporarily halted before the late September restart.

Will the Boilermakers understand basic concepts and their assignments? Or will confusion lead to game-breaking mistakes? Has Purdue had enough time to get a good feel for what Diaco wants? Only time will tell.

5. Just play

When Purdue lost its veterans last season — Lorenzo Neal didn’t play after an ACL injury at the end of 2018 and Markus Bailey injured his knee early in the year — it lost its edge. The Boilermakers played tight, hoping to not make mistakes rather than aiming to make plays. It’s understandable with a largely inexperienced group. But it’s not a recipe for solid defensive play.

Diaco needs to instill confidence in a group that had been battered the last couple years, and that won’t be easy. The return of Neal, a big and impactful nose tackle, helps significantly. And Karlaftis is a proven athlete who plays with confidence and swagger. But who else will?