Brian Kelly says Notre Dame's goal for this season has always been a national championship. (1:05)

SOUTH BEND, Ind. -- Mike Elko doesn't love to yell. He will do it, if needed, but he would rather teach defense through the whys and the hows.

Elko is an inquisitive coach who likes inquisitive players. He wants Notre Dame defenders to ask why a play worked or how to read a certain formation, why a position switch will help or how to leverage an offensive lineman. Elko's goal is a defense that takes the field with comfort in the scheme and the calls and with detailed understanding of opposing offenses.

"How are we doing things? Why are we doing things? You have to be able to teach these kids conceptually," Elko told ESPN.com this summer. "If they can't learn concepts, they're constantly going to be seeing things that they don't understand. You're asking them to do things that make sense to them. You're explaining why.

"[If] they feel they can do what you're asking, then they start having success."

Notre Dame's success on defense under Elko is the single biggest reason the team finds itself in the top 10 and in the hunt for its first College Football Playoff berth, a year after going 4-8. Elko, plucked from Wake Forest by coach Brian Kelly to repair a disjointed unit, has the Irish taking the ball away (17 turnovers forced, tied for eighth nationally), keeping rushers out of the end zone (one rushing touchdown allowed, first nationally) and limiting points (16.4 PPG allowed, 12th nationally).

Brian Kelly, left, came away impressed after Mike Elko's Wake Forest defense held Notre Dame to 282 yards and 15 first downs in 2015. Matt Cashore/USA TODAY Sports

Through seven games, the Irish already have three more takeaways and four more sacks than all of last season. They are one of six FBS defenses to allow opponents to score touchdowns on less than 40 percent of their red zone possessions. They are thriving with a depth chart not packed with future NFL draft picks.

"For those that watched us last year compared to this year, we didn't trade for anybody," Kelly said after Notre Dame's 49-14 win over USC on Saturday. "There was nobody on the waiver wire."

Only Elko. The upgrades for Notre Dame's defense continue to grow. But it's important to know why and how things have changed. Not to mention: Who is this guy pulling the strings?

Knowledge seeker

For 15 minutes at every practice, every Notre Dame defender goes through ball-disruption drills. Even the linemen.

"At first, we were like, 'Aw, that's kind of nitpicking,'" defensive end Khalid Kareem said. "But then it showed in the games. It worked."

Elko doesn't do the drills to torture players. He structures everything with an educational purpose.

He has found that if players know why they're drilling something, even something basic, they respond better. When they make great plays, they need to differentiate between being lucky to be in the right spot and visualizing how and why they got there.

"Players buy into what he says because it's not just about the moment," said linebackers coach Clark Lea, who came with Elko from Wake Forest. "It's about the teachable moment. And he always circles back with a lesson involved."

Kelly's response Tuesday to a question about linebacker Te'von Coney's improvement -- "He's trusting the teaching" -- could apply to just about any of Elko's players.

Elko came to Notre Dame as one of only two FBS defensive coordinators with top-40 defenses in each of the past five years (at Wake Forest and Bowling Green). He's quick to note he had more talent than many think, especially at Wake -- linebacker Marquel Lee is starting for the Oakland Raiders as a rookie, Duke Ejiofor is the No. 3-ranked senior defensive end on Mel Kiper's board.

"We had lower-recruited players, but we had some good players," Elko said. "We taught a defense that they understood, and we weren't asking kids to just make plays and do things that they weren't capable of doing."

Going from Wake to Notre Dame would seem like a no-brainer for a coach, but before accepting Kelly's offer, Elko studied the personnel. He wouldn't come if the defense looked years away from breaking through. He saw enough potential, especially among the younger classes, to make him believe he could flip it.

After arriving, he made some key adjustments. He shifted Drue Tranquill, the team's No. 2 tackler in 2016, from strong safety to rover, a safety/outside linebacker hybrid, where his skills better fit. Tranquill, slightly heavier but actually faster, leads the team in tackles for loss (5.5) and fumble recoveries (three), adding a forced fumble, an interception and a sack.

There were also more subtle tweaks. Kareem, one of three players with three sacks, is playing more on the outside, rather than alternating from an interior position.

"It lets me be the edge rusher I was before," Kareem said. "It allows me to play my game."

An evolving scheme

Coaches who studied Notre Dame's defense the past few years saw a unit lacking identity. One head coach told ESPN.com last fall that the Irish ran so many styles, he didn't know how the players could keep it all straight.

Here's what offensive coordinators are saying about the Irish defense now:

"Tremendous. Great scheme. Guys play hard. Few busts. Makes you earn any scoring drive."

"They are very sound in what they do. The big thing is that the players understand it and they can play fast."

After Notre Dame held USC to 14 points and forced quarterback Sam Darnold into mistakes when he wasn't running for his life, the easy response would have been to dial up the same plan for NC State. That's not Elko.

"Mike's greatest strength is his ability to adjust," said Wake Forest coach Dave Clawson, who had Elko on staffs at four schools. "He always understood how players dictate the scheme; the scheme doesn't dictate the players. With [Ejiofor], he constantly moved him to get a good matchup with the pass rush. It wasn't, 'He's an end. He's gotta win.' It was, 'Hey, we're going to find a way to get him isolated.'"

Elko's system is constantly changing. He expects coaches to come to meetings with opinions and ways to challenge him on certain strategies.

If Lea doesn't feel good about how a linebacker is being used or how to fit a certain run play, he immediately goes to Elko.

Linebackers coach Clark Lea says Mike Elko's defensive philosophy is "about the teachable moment. And he always circles back with a lesson involved." Fred Kfoury III/Icon Sportswire

"You have to be a thinker; you can't just be OK with the status quo if it's not going to help your players," Lea said. "We don't ever want to put our players in a position where the answer is: Just play faster or play harder."

Added Elko: "What [players] appreciate is a scheme that they can understand, a scheme they felt confident in their ability to execute, a scheme that allowed them to get lined up quickly and play."

Elko sees game plans as a constant chase. The influx of run-pass option, spread concepts and tempo has offenses running more plays and rarely repeating them. Offenses don't show as many tendencies, but he latches on to the ones he sees.

Notre Dame defenders knew Darnold was "loose with the football," end Daelin Hayes said. When Darnold dropped the first snap of the game, Coney was there to pounce on it. Kareem said he knew USC's offensive tackles were "leaners," allowing him to beat them to the outside. Hayes saw USC right tackle Chuma Edoga had been repeatedly beaten on the inside the week before against Utah, so he used speed to get Edoga to overset, allowing Hayes to scoot by.

"Guys are truly buying into the process," Hayes said, "becoming a great, detailed defense. That has been huge."

Book smart, street smart

In 2015, Notre Dame had a strong, balanced offense. The Irish averaged 7 yards per play and eclipsed 400 yards in every game but one. Elko's Wake Forest defense held Notre Dame to 282 yards and 15 first downs, also a season low.

It stuck with Kelly.

The coach also tracked how Elko's defenses forced takeaways and pressured quarterbacks, areas in which Notre Dame struggled in 2016. Kelly liked how Elko came up through college football's back roads, the FCS and lower divisions. Kelly didn't reach the Power 5 until his 25th year in coaching.

"It really is an indicator of your ability to teach and communicate," Kelly said, "and do more with less."

After finishing college at Penn, where he played safety, Elko started his career at Stony Brook, which he calls one of two true destinations (Albany is the other) for aspiring East Coast coaches who want to get their feet wet. His title read graduate assistant. In reality, he coached the linebackers.

In 2001, he landed his first coordinator job at the U.S. Merchant Marine Academy, a Division III program on Long Island, before joining Clawson at Fordham the following year.

"That was the first glimpse of where my vision of football was going to go," Elko said. "That staff was living in the Bronx. We were young, hungry, smart, willing to work."

In Elko, Clawson saw a curious, instinctive coach who could relate to anyone. Sure, Elko had an Ivy League degree, but he didn't hang out with "the eating club group." He spent most of his free time playing pickup basketball around Philly.

Elko spent 12 of the next 15 years with Clawson, who saw Elko in various roles: position coach, recruiting coordinator and defensive coordinator.

"Mike is book smart and street smart," Clawson said. "A lot of coaches can get up there and draw plays up and tell you what they do. They can't understand why they do it. Mike always understood that."

Because of the mostly off-the-radar path, Elko, 40, wasn't a splashy hire at Notre Dame. But much like Don Brown at Michigan, the move resonated in coaching circles. There's less surprise about Notre Dame's surge among those in the know.

The Irish players aren't shocked, either. They understand how they got here, where they're going and why they'll get there. Elko wouldn't have it any other way.

"The roof," Kareem joked when asked about the ceiling for Notre Dame's defense. "We're just playing free, just going after the ball and playing our ball."