A Look at 11 Possible Candidates to Replace Jim Knowles As Ohio State’s Defensive Coordinator

With Jim Knowles’ decision to leave Ohio State for Penn State on Sunday, the Buckeyes must now find his replacement. Whoever replaces Knowles will inherit a defense that ranked No. 1 in the FBS this past season but will be replacing eight starters, though it will be led by college football’s best safety in Caleb Downs.

As Ohio State’s defensive coordinator search officially begins, we take a look at 11 potential candidates who could warrant consideration from the Buckeyes. We start with the two current staffers who could be candidates for the job, followed by five external candidates who could make sense for the Buckeyes based on their coaching history and/or Ohio State ties. Finally, we look at four coaches who are likely long shots to become Ohio State’s defensive coordinator but who Ryan Day should call nonetheless to see if they’d be interested.

Internal Candidates

Matt Guerrieri, Ohio State safeties coach

The early rumor is that Guerrieri could be the leading candidate to replace Knowles, which makes Day’s comments about Guerrieri during Sunday’s national championship celebration seem notable.

“One of the brightest minds in college football, and I’m telling you, a star in the making,” Day said while introducing Guerrieri to the crowd.

“One of the brightest minds in college football and I’m telling you a star in the making our safeties coach Matt Guerrieri”

Matt Guerrieri gets quite the shoutout after his first season with the Buckeyes. He was co-defensive coordinator last season with Indiana: pic.twitter.com/3eIw899yUu

— Adam King (@AdamKing10TV) January 26, 2025

Guerrieri was brought to Ohio State because of his ability to coach Knowles’ system, which could make him a natural heir apparent if the Buckeyes choose to prioritize continuity. Promoting Guerrieri would allow Ohio State to continue running the same defensive scheme that it used to win a national championship this past season while also keeping a sense of familiarity with its defensive players rather than forcing them to learn how to play for a new coordinator. And it’s a move that would likely come with the endorsement of Downs, who earned unanimous All-American honors under Guerrieri’s tutelage this past season.

Guerrieri was the lead defensive play caller at Indiana in 2023 and was also previously the co-defensive coordinator at Duke from 2018-21. His results in those roles weren’t spectacular – none of those defenses ranked in the top 50 nationally in total defense or top 70 nationally in scoring defense – but he’s also never had the opportunity to call plays for a defense with anywhere near the talent he’d have at his disposal at Ohio State.

Tim Walton, Ohio State secondary coach

The other internal candidate to replace Knowles would be Walton, who has experience as a defensive coordinator in both college football (Miami in 2007, Memphis in 2008) and the NFL (St. Louis Rams, 2013).

Having firmly established himself as one of college football’s elite secondary coaches over the past three years at Ohio State, Walton has a résumé that would befit a promotion with three decades of coaching experience in either the NFL or the FBS. His defensive backs have led the way for Ohio State’s pass defense to be the best in the country for each of the past two seasons, while he’s also emerged as one of college football’s best recruiters.

Promoting Walton to defensive coordinator would likely be a popular move among both players and coaches inside the Woody Hayes Athletic Center. It’s been more than a decade since Walton has been a defensive play caller, however, so he might be best suited to remain in his current role and continue to focus on developing Ohio State’s defensive backs to be the “Best in America.”

Logical Possibilities

Jim Leonhard, Denver Broncos defensive pass game coordinator

Wisconsin consistently had elite defenses during Leonhard’s tenure as the Badgers’ defensive coordinator from 2017-22, ranking in the top 11 nationally in total defense in all but one of his six seasons in that role.

Leonhard has spent the past year in the NFL as the defensive pass game coordinator and defensive backs coach for the Denver Broncos, helping lead a defense that ranked third in the NFL in points allowed per game.

Day has tended to favor hiring coordinators with NFL experience, so Leonhard’s combination of NFL experience and proven track record as a collegiate defensive coordinator would make him an appealing choice to replace Knowles if he’s interested in returning to the collegiate game.

Randy Bates, Pittsburgh defensive coordinator

An Ohio State alumnus, Bates has been the defensive coordinator at Pittsburgh since 2018. His defenses with the Panthers have consistently ranked as above average, including three defenses that ranked in the top 25 in total defense in 2019, 2020 and 2022, though his 2024 defense finished just 81st in the FBS with 378.2 yards allowed per game.

Bates was previously Northwestern’s linebackers coach for 12 seasons, giving him plenty of familiarity with the Big Ten, and he previously worked alongside Kelly when he was the linebackers coach at New Hampshire – Day’s alma mater – from 1992-97.

Jerod Mayo, former New England Patriots head coach

Considering Day hired not one but two former NFL head coaches (Bill O’Brien, then Kelly) when filling its offensive coordinator position last offseason, it stands to reason that such experience could be a valued commodity in Day’s defensive coordinator search, too.

Mayo’s tenure as the New England Patriots’ head coach was short-lived, as he was replaced by former Ohio State star Mike Vrabel after just one season in which the Patriots went 4-13. Before that, however, Mayo was highly regarded as one of the NFL’s top young assistant coaches during his five years as the Patriots’ linebackers coach, serving as the de facto co-defensive coordinator for multiple years in that role.

It’s uncertain whether Mayo would be interested in coaching at the collegiate level, as he’s only coached in the NFL, but he is still looking for a new opportunity.

Jon Heacock, Iowa State defensive coordinator

The younger brother of former Ohio State defensive coordinator Jim Heacock, Jon Heacock has been the defensive coordinator at Iowa State for the past nine years. Each of his last eight defenses have ranked within the top 52 nationally in both total and scoring defense, including a pair of top-10 seasons in total defense in 2021 and 2022.

An Ohio native who worked for Jim Tressel at Youngstown State and then succeeded Tressel as the Penguins’ head coach for next year, Heacock’s ties to Ohio State could get his name in the mix for this job.

Mike Tressel, Wisconsin defensive coordinator

Another experienced defensive coordinator with Ohio State ties, Tressel has a consistent track record of leading successful defenses across his tenures at Wisconsin, Cincinnati and Michigan State. The nephew of Jim Tressel, Mike Tressel’s defenses as a defensive coordinator or co-defensive coordinator have always ranked in the top 50 nationally in total defense, including two top-10 defenses at MSU and one at Cincinnati.

Hiring him wouldn’t be as flashy as hiring his boss at Wisconsin, but he has the qualifications and name to warrant consideration.

Worth A Call

Jeff Hafley, Green Bay Packers defensive coordinator

Hafley might not be inclined to return to the college game after leaving his post as Boston College’s head coach a year ago to become the defensive coordinator of the Green Bay Packers, but Day should at least gauge his interest in returning to Columbus.

Ohio State had the best defense in the country in Hafley’s lone season as its co-defensive coordinator and lead defensive play caller in 2019, Day’s first year as OSU’s head coach. His history of working alongside Day both at Ohio State and in the NFL would make for a smooth transition for both parties, and he continued to show his mettle as a defensive coordinator in the NFL this season as the Packers ranked sixth in the league in both points and yards allowed per game.

Luke Fickell, Wisconsin head coach

This is probably an even longer shot than convincing Hafley to return to Ohio State, but it’s another call that’s at least worth making.

An Ohio State alumnus who was previously defensive coordinator from 2005-10 and 2012-16 with a year as OSU’s interim head coach in between, Fickell would bring a proven track record of success in that role for the Buckeyes as well as eight years of head coaching experience.

Fickell is poised to make nearly $8 million a year as Wisconsin’s head coach in 2025, so it would come as a big surprise if he stepped away from that job to return to coordinating. But Ohio State already plucked a sitting Big Ten head coach to become one of its coordinators when it hired Chip Kelly to run the offense last offseason, and Fickell’s seat could be heating up in Madison after a 5-7 season in 2024, perhaps opening the door slightly that Ohio State could bring him home with a lucrative offer.

Phil Parker, Iowa defensive coordinator

Parker has worked alongside Kirk Ferentz at Iowa since Ferentz became Iowa’s head coach in 1999, so it would come as a surprise if Parker left to become a defensive coordinator elsewhere after 25 years with Ferentz and the Hawkeyes. 

Like with Hafley and Fickell, though, Day would be smart to pick up the phone and at least see if Parker’s interested. The Lorain, Ohio native has long been regarded as one of college football’s elite defensive coaches, with Iowa ranking in the top 20 in scoring defense in each of the last 10 consecutive seasons.

Glenn Schumann, Georgia defensive coordinator

Schumann has been regarded as one of college football’s top young defensive coaches for several years as Georgia’s defenses have consistently been among college football’s elite with Schumann serving as the Bulldogs’ co-defensive coordinator from 2019-23 and as its sole defensive coordinator this past season.

It would come as a big surprise if the Georgia native left the Bulldogs to become a defensive coordinator somewhere else, but Ohio State has the cachet that few other schools do to potentially pull an assistant away from another power program. After Penn State poached Knowles away from Columbus, it could be worth a shot for Ohio State to see if it can put together an offer that would entice Schumann to leave Athens.