Ohio State head football coach Ryan Day was the reason defensive coordinator Jim Knowles left for Penn State this offseason.

Penn State announced Monday it had hired Jim Knowles as its defensive coordinator. According to multiple reports, Knowles reached a three-year contract with an average annual salary of $3.1 million. Knowles is a Philadelphia native. In a statement, Knowles said he was "excited for this opportunity" to join the Nittany Lions' program.

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