Cosh served as defensive coordinator and linebackers coach for the Wildcats since 2009. Kansas State improved in a big way in 2011, cutting almost 100 yards per game off of their rushing defense to rank 37th nationally.
Holtz and Cosh worked together as assistants at South Carolina under Lou Holtz from 1999 to 2003. In all, Cosh has been a defensive coordinator for 15 of his 28 seasons as an assistant, with stops as well at Maryland, Michigan State and Illinois.
"I'm excited that Chris has agreed to be the defensive coordinator here," Holtz said in a statement. "We're very familiar with each other, having coached together for five years at South Carolina. I've got great respect for him as a teacher and communicator. He's had a lot of success building some of the top programs in the country and I'm looking forward to working with him again here at USF."
The Bulls return seven starters and are hoping to rebound from a disappointing season in which they lost five games by six points or fewer. They have five of their top six leading tacklers returning from a group that simply needs to be more consistent.
Cosh will be South Florida's third defensive coordinator in four years, so it remains to be seen how another coach will affect the unit's continuity.
Andrea Adelson covers Big East football for ESPN.com.