As Ryan Day looks to hire his fourth defensive coordinator in seven seasons, here are potential candidates to replace Jim Knowles.

Knowles, a Philadelphia native with strong ties to the Northeast, transformed the Buckeyes' defense during an impressive three-year stint. Ohio State ranked top three in total defense each of the past two seasons and led the nation by holding opponents to 254.6 yards per game and 4.2 yards per play during a historic campaign.

COLUMBUS, Ohio — Ohio State football coach Ryan Day had praise for defensive coordinator Jim Knowles on Sunday. While speaking at the Buckeyes' championship celebration inside Ohio Stadium, Day gave Knowles a shoutout and mentioned the defense’s dominance throughout the College Football Playoff.