NFL Network's Mike Garafolo first reported the hire.
The Chiefs began looking for a new coach to lead their defense after Bob Sutton was fired on Jan. 22. The three-time defending AFC West champions struggled on that side of the ball in 2018, finishing 24th in points allowed (26.3 per game) and 31st in yards allowed (405.5).
One common criticism levied at Sutton is he routinely failed to make adjustments during games, opting to stick to his formula even when opponents were able to move the ball with ease.
Per ESPN's Adam Schefter, Spagnuolo emerged as a favorite for the job in part of his relationship with Andy Reid. He worked as an assistant with the defense in several capacities for eight seasons under the Chiefs head coach with the Philadelphia Eagles from 1999 through 2006.
After the 2011 season, Reid told reporters he tried to bring Spagnuolo back to the Eagles in an unspecified role.
The hiring of Spagnuolo will likely force the Chiefs to alter their defensive roster. He primarily utilizes a 4-3 base, compared to the 3-4 scheme used by Sutton.
After taking 2018 off, Spagnuolo returns to the NFL with one of the best situations possible. Kansas City proved last season it can be successful with a suspect defense—it went to overtime in the AFC Championship Game before losing to the New England Patriots.
As long as Spagnuolo puts together a scheme that maximizes the talent he has and adjusts his plan during games if opponents seem to have them figured out, the Chiefs will be in much better position to have a defense that contains teams long enough to let Reid's high-powered offense light up the scoreboard.