Unable to capture the magic of the 2017 season, Purdue made a change at the top of its defensive coaching staff during the offseason.

Out was Nick Holt, the co-defensive coordinator who helped engineer the Boilermakers’ turnaround at the start of Jeff Brohm’s tenure in ’17, and in was Bob Diaco, the former DC at Cincinnati, Notre Dame and Nebraska who is charged with reenergizing the Boilermakers’ defense.

His vision is a base 3-4 — the veteran coach, however, would prefer to refer to it as a multiple-base front — which represents a significant change for Purdue, which had been a 4-man front under Holt and for years previously.

But it’s a new era.

There’s reason to change. Since 2017, when Purdue had a more respectable outfit in helping it to a 7-win season, the defense has gradually fallen back, to the point where it ranked 12th among B1G teams in scoring (30.6) and 13th in total yardage (436.3) last season. Not all was on Holt; Purdue suffered mounting injuries last season too, arguably to its 2 best defenders in tackle Lorenzo Neal and linebacker Markus Bailey.

Neal, who missed the season after suffering a knee injury at the end of the ’18 season, is back, ready to reclaim his place as one of the top interior D-lineman in the Big Ten. He’s a good centerpiece at the nose of a 3-4.

But Bailey departed to the NFL. And while Diaco has solid pieces, like potential star George Karlaftis, placing them into his preferred system is still a work in progress. Not having an entire spring camp didn’t help, either.

What should we expect in 2020?

Let’s play better or worse.

Pressuring the QB: Better

For too long, finding a consistent rush had been a problem for the Boilermakers, who finished 12th in the B1G with 23.0 sacks last season.

Individually, George Karlaftis helped to solve that — finally — in 2019, when the freshman All-American became the first Boilermaker edge rusher to have more than 5.5 sacks in a season since Ryan Kerrigan had 12.5 in 2010. Now, Karlaftis will try to increase his productivity, after having 7.5 sacks last season, but doing so now as the D-end in a 3-man front.

Look for Diaco to scheme to free up the 6-4, 265-pounder for as many 1-on-1 battles on the perimeter as possible. But Karlaftis wasn’t Purdue’s only threat last season, as fellow end Derrick Barnes also turned in a 7.5-sack performance.

Barnes, who came to Purdue as a linebacker, moves back to the position. He’s slated on the interior — the 7 spring practices before COVID-19 at least gave him a precursor to his new assignments — so his duties in rushing the passer might be reduced.

So where does Purdue turn?

When Neal was healthy in ’18, he showed he could get push in the middle of the line, picking up a sack and 3 tackles for loss. But the Boilermakers, even though they are short on experienced linebackers, will have to bring heat from there as part of the 3-4.

Maybe Jalen Graham can develop into such a threat. The sophomore was mainly a defensive back as a true freshman, playing some safety and a bit of nickel. But he seems most suited for playing in the box, so Purdue has moved him to an outside linebacker spot. Newcomer DaMarcus Mitchell, a massive 6-3, 260-pound transfer from Southwest Mississippi CC, will play opposite, perhaps moving down to the line on occasion to rush off the edge.

Ideally, Diaco would like to be able to pressure from multiple locations, keeping the offense off-balance, and perhaps with many eyes on Karlaftis, it’s a plan that can work.

Run defense: Same

In the Big Ten West, it’s imperative to be able to slow the rush.

Purdue couldn’t last season, ranking 12th in the Big Ten in rush defense, allowing 192.5 yards on the ground. It was ugly at times, like the 403 given up to Wisconsin. They also allowed 25 rushing TDs, 12th-most in the B1G.

Some might be excusable; after all, the Boilermakers were without their top interior lineman and linebacker. But those holes only compounded the others, and the Boilermakers couldn’t compete.

Now, Purdue will have to do so out of the new defense, which puts a lot of pressure on largely untested linebackers, where not only are the starters a question — Purdue needs four of them — but the depth even more so.

Purdue thinks its D-line will be bigger and stronger, and there’s reason to think that could be true, with Neal and fellow senior Anthony Watts, as well as Karlaftis. And the secondary, which has been a sore spot, spent the offseason changing over personnel, which should help matters as well.

Pass defense: Better

Purdue brought in a couple of transfers as part of an overhaul to its secondary, a change that the Boilermakers hope leads to better results.

Because the results last season were poor, to say the least. Purdue was gashed through the air, allowing 243.8 yards per game with only 9 interceptions against 20 touchdowns.

Senior Tyler Coyle, a graduate transfer from UConn, is an immediate upgrade at safety, where Purdue has talent but it’s largely inexperienced. Marvin Grant, who sat out his freshman season with an injury, could factor in now. But Coyle was productive for the Huskies, leading UConn in tackles 2 of the past 3 seasons.

The other transfer, D.J. Johnson from Iowa, is hoping to play right away, after leaving the program after a falling out with the coaching staff. Perhaps he has a solid argument for immediate eligibility, but the NCAA has yet to rule.

Those are the transfers into the secondary.

Purdue saw them leave, too, the most notable being former starting cornerback Kenneth Major. But there are more options at corner, like experienced Dedrick Mackey and Cory Trice, the latter who showed great moments at times as a true freshman — like his 2-pick game vs. Maryland — but looked lost others.

Special teams: Better

Purdue rolled with a 2-punter rotation last season, mainly because true freshman Brooks Cormier didn’t show the consistency Brohm wanted.

The kid can boom it, but lowering the throttle was a bit of a problem. Perhaps in his second year, the big 6-5, 215-pounder can show he’s ready to take over the job full-time.

Last year, Cormier punted in 9 games, hitting for an average of 40.2 yards per attempt.

Overall: Better

If Purdue is to take a step forward, it won’t all be on an offense that could be one of the most explosive in the Big Ten.

The defense must contribute, too. And Diaco, who shares the title with co-defensive coordinator title with secondary coach Anthony Poindexter, will be charged with transforming the Boilermakers into a more balanced group.