In a move that has shaken the college football world, Jim Knowles, Ohio State defensive coordinator for the past three years, has decided to leave the Buckeyes and join Penn State. Fresh off a national championship season, Ohio State now faces the challenge of finding a new leader for its defense a task head coach Ryan Day is no stranger to.
Transforming Ohio States Defense
Knowles arrived at Ohio State in 2022 and quickly turned a struggling defense into one of the best units in college football. In 2021, prior to his arrival, the Buckeyes ranked 38th in scoring defense, 97th in passing defense, and 59th in total defense. Under Knowles, the defense steadily improved, culminating in a dominant 2024 campaign where Ohio State finished first in total defense, third in scoring defense, and third in rushing defense.
While Knowles impact on the Buckeyes was undeniable, his tenure was not without challenges. Early on, the defense struggled with giving up explosive plays, most notably in losses to Michigan and Georgia in 2022. However, adjustments made over the next two seasons helped eliminate those vulnerabilities, transforming the Buckeyes into a unit capable of delivering a national championship.
Why Did Knowles Leave?
Knowle  departure has sparked speculation and controversy. Reports suggest tension within the coaching staff may have played a role, with some sources claiming that Knowles initiated contact with other programs and stopped communicating with Ohio State despite efforts to retain him. Allegedly, head coach Ryan Day asked Knowles not to attend the Buckeyes  national championship celebration, further fueling rumors of a strained relationship.
Players reportedly felt blindsided by the decision, with some alleging Knowles had assured them he would return for the 2025 season. Regardless of the circumstances, Knowles leaves behind a lasting legacy, having been instrumental in Ohio State turnaround on defense and its recent championship triumph.
Finding the Right Replacement
Ohio State now begins the search for a new defensive coordinator, with Day likely to consider both internal and external candidates.
Internal Options
Two Buckeye assistants with defensive play-calling experience could be in the mix.
1. Matt Guerrieri: Ohio States safeties coach, Guerrieri, has extensive experience as a defensive coordinator, serving in that role at Duke and Indiana. A part of Knowles, Guerrieri has been praised for his football acumen, and Day singled him out during the championship celebration, calling him “one of the brightest minds in college football.
2. Tim Walton: The secondary coach and Ohio State alumnus also brings a wealth of experience, having called defenses for Miami (FL), Memphis, and the St. Louis Rams. Known for his ability to recruit and develop players, Walton is well-respected among the team and could be a strong internal candidate.
External Candidates
If Day looks outside the program, several intriguing options are available:
Jim Leonhard: A former Wisconsin standout and defensive coordinator, Leonhard has a track record of success in the Big Ten. After serving as the Denver Broncos  defensive backs coach, his expertise in forcing turnovers and building elite defenses makes him a natural fit.
Jeff Hafley: The current Green Bay Packers defensive coordinator and former Ohio State co-defensive coordinator could return to Columbus. Hafley 2019 Buckeye defense was one of the best in the country, and his familiarity with the program could make him an ideal candidate.
A New Chapter for Ohio State
Replacing Knowles will not be an easy task, especially with nine defensive starters set to leave in 2025. However, Day has proven adept at finding top-tier replacements in the past, and the program prestige ensures Ohio State will attract high-caliber candidates.
Whether the next defensive coordinator comes from within the program or is an outside hire, the Buckeyes are poised to continue their tradition of defensive excellence. As for Knowles, his contributions to Ohio State will be remembered, even as he begins a new chapter at Penn State.
