Head coach Ryan Walters' defensive background is a noticeable change from Purdue's traditional focus on high-powered offense. 

The former Illinois defensive coordinator is now the youngest head coach in the Big Ten at 36 years old, and was a finalist for the Broyles Award – given to the top assistant coach in the country – this season.

The Illini defense under Walters ranked as the No. 1 scoring offense and second in yards allowed per game in the country.

Walters is the first defensive coordinator turned Purdue head coach since Joe Tiller, who served as the Boilermakers’ defensive coordinator from 1983-86, but is primarily known for his work on the offensive side of the ball.

The last Purdue head coach to not have offensive experience, and the last one without head coaching experience, was Leon Burtnett. Burtnett coached for five seasons, 1982-86 and amassed a 21-34-1 record before resigning as head coach.

At Illinois, Walters’ defense was usually a 3-4 scheme, meaning three players on the line of scrimmage and four players off the line, not counting the defensive backs. The scheme features three linemen and two inside linebackers in the “box,” which is the area between the offensive tackles extending five yards past the line of scrimmage, and two outside linebackers outside of that box.

The scheme differs from the 4-2-5 scheme Purdue ran under Jeff Brohm, which features two defensive tackles and two outside linebackers on the line of scrimmage, two traditional linebackers in the box, and one safety-linebacker hybrid amongst the four other defensive backs.

The shift from the 4-2-5 to a traditional 3-4 means the loss of one player on the line of scrimmage, but it’s supplemented by the addition of two more linebackers off the line. In a 3-4 scheme, much of the pass rush is expected to come from those two linebackers, especially on the quarterback’s blind side.

The defense is also predicated on having a large defensive tackle, often called the nose tackle, filling/covering both “A” gaps, between the center and his surrounding guards. The nose tackle is responsible for tying up blockers and allowing the other defenders to get past the offensive line.

Aside from his 3-4 defense, Walters mixed in other schemes, switching to a 4-3 and even bringing in five defensive linemen for a 5-2 scheme depending on the opponent and situation. He did run a base 4-3 scheme while at Missouri. 

"Offenses are becoming a lot more multiple in different formations and getting diverse with the plays,” Walters said in a press conference during his first year as defensive coordinator. “You see the natural progression that defenses have to be multiple too. It is hard to label a defense, at least the systems that I have been a part of. We are a cookie cutter 4-3 or we are a 4-2-5 or we are a 3-4.

“The goal is to be all three of those at any given moment in time, especially the early downs.”

Walters is the one who caused now-fired Nebraska head coach Scott Frost to infamously admit to throwing out half of his game plan when the Illinois lined up with four defensive linemen, when Frost expected just three. The Illini won in their first game under Walters, defeating the Cornhuskers 30-22.

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