EVANSTON, Ill. — A year ago, Ryan Field would have resembled a crime scene, with yellow caution tape surrounding Ohio State’s defense and white chalk outlining the Buckeyes’ missed tackles.

You know the story by now. Silver Bullets? The 2018 defense shot blanks, allowing big plays and big points — 25.5 per game; a dubious school record.

For Buckeyes fans, the carnage was hard to watch, not only because of the frequency — 39 “chunk plays" of 30 yards or more, including seven of at least 70 yards — but because the perpetrators were not the usual suspects. This was not Alabama, Oklahoma and Clemson slicing up the defense, but Oregon State, Indiana and Maryland.

Ohio State ranked 120th out of 130 FBS teams in long scrimmage plays — 10 yards or more — allowed. Now? The Buckeyes entered Friday’s game against Northwestern tied for 12th. They have not allowed a play longer than 56 yards, and after mauling the Wildcats 52-3, the defense should remain in the top 15 when the dust settles following today’s full slate of games.

Putting the defensive turnaround in perspective, through seven games Ohio State tailback J.K. Dobbins has four runs of 50 yards or more. The Buckeyes defense has allowed their seven opponents only one (56 yards by Nebraska quarterback Adrian Martinez).

Players and coaches avoid talking about last season. Too traumatic. But read between the lines and a picture emerges of a defense that did not know if it was coming or going. So it did neither, frozen in place as running backs and receivers ran free.

“The (big plays) went down because everyone is out there playing freely. We’re not worried about giving up a play or making a play,” cornerback Damon Arnette said after Ohio State limited Northwestern to 47 yards passing — the Wildcats rushed for 157 — and no plays of more than 16 yards.

Arnette’s conclusion echoes what safety Jordan Fuller said earlier in the week.

“You don’t feel like you’re making a one-on-one tackle as much when you have other guys surrounding the ball,” Fuller said. “You feel like you can take your shot.”

The best defenses play fast, which means playing unencumbered mentally by avoiding paralysis by analysis. For whatever reason, whether because of overly complicated schemes or fear of failure — much of that fear having to do with facing unforgiving coaches — the 2018 Buckeyes bombed out defensively.

Coach Ryan Day knew things had to change when he took over for Urban Meyer in January. He dipped into the NFL to get defensive co-coordinator Jeff Hafley and wooed linebackers coach Al Washington Jr. and defensive co-coordinator Greg Mattison from Michigan, then sat down to determine what single weakness needed to change.

Conclusion: Limit chunk plays, or “explosives,” as Hafley calls them. Explosives are to defenders what hand grenades are to foxholes. They create a “wait for it” mentality that leads to an expectation of ruin.

“We did a good job again, for the most part,” Hafley said of Friday’s performance. “In the pass game we kept the ball in front of us. And no touchdowns. We always have a goal to get a fourth-quarter shutout. That’s important to us. You could see the older guys were excited when the younger guys went and did that.”

Day and Hafley saw Thursday during practice and at the team hotel how locked in the defense was.

“And when we woke up (Friday) they had a look in their eye. And in the locker room when I addressed them. I felt pretty good about it,” Hafley said. “This group is special. They have an edge. It’s fun to be around them.”

Hafley has talked of how during the offseason the defensive emphasis was on limiting big plays.

“Schematically, the No. 1 thing we talk about — we’ll say it over and over again — is we want to eliminate explosives,” he said.

For that to happen, the defensive coaches focused on lowering risk, even if it resulted in a potentially smaller reward.

“If we think a blitz is really good but there’s potential for it to result in an explosive, we’re not going to put it in,” Hafley said. “Our whole philosophy is we want to make you drive the length of the field. If you can put it in the end zone against us in the red zone, then nice job.”

Other factors that contribute to reducing chunk plays include improved tackling and getting more defenders to the ball. The Buckeyes (7-0) are excelling in both areas. They share the lead nationally in allowing only four chunk plays of 30 yards or more all season.

One year later, few defensive crimes have been committed.

roller@dispatch.com

@rollerCD