Penn State has hired Ted Roof to be its new defensive coordinator.
Roof will reunite at Penn State with new Nittany Lions coach Bill O'Brien, who was introduced Saturday in State College. O'Brien served as Duke's offensive coordinator under Roof in 2005-06. Roof spent a year as Minnesota's defensive coordinator in 2008.
O'Brien is retaining two defensive assistants from the previous Penn State staff in defensive line coach Larry Johnson and linebackers coach Ron Vanderlinen.
Longtime Nittany Lions defensive coordinator Tom Bradley, who served as interim coach following Joe Paterno's firing, isn't expected to remain on staff.
Penn State hasn't officially announced any of O'Brien's assistants. In addition to Roof, Vanderlinden and Johnson, Tennessee Titans assistant Charles London has said he's joining the staff.
Other reported additions include Ball State offensive line coach John Strollo, Buffalo Bills wide receivers coach Stan Hixon and former Texas offensive line coach Mac McWhorter.
O'Brien on Sunday told ESPN.com that at least seven assistant coaches will be in place by Wednesday.
O'Brien has rejoined the New England Patriots, where he'll remain as the team's offensive coordinator throughout the NFL playoffs.
Adam Rittenberg covers Big Ten football for ESPN.com. He can be reached at firstname.lastname@example.org