DETROIT -- Matt Patricia is reaching back to his New England Patriots roots for the Detroit Lions' new defensive coordinator.
The Lions hired Philadelphia Eagles defensive backs coach Cory Undlin on Monday to run their defense. ESPN first reported the hiring.
Undlin spent the past five years with the Eagles, but got his start in the NFL as a defensive assistant with the Patriots in 2004, the same year Patricia entered the league as a coaching assistant in New England.
He initially will not call plays for the Lions, according to the Philadelphia Inquirer.
The Lions beat the Eagles for one of their three wins this season, and before the game Patricia referenced his friendship with Undlin and the mix of coverages they use in the secondary.
"They've had a couple moving parts back there, and I think those guys are just trying to understand the techniques that they're teaching," Patricia said. "Cory Undlin, who actually coaches the secondary, is a good friend of mine and I know he's got those guys working really hard."
Undlin, 48, replaces Paul Pasqualoni as defensive coordinator, though Patricia ran much of the defense this season when the Lions were in the bottom third of the league in most categories.
They finished 31st in total defense, allowing their most yards (400.4 per game) since their winless season of 2008; were 26th in points allowed (26.4 ppg); were last against the pass (284.4 ypg); and blew second-half leads in seven of their 16 games.
The Eagles, who won the NFC East this season and lost in the wild-card round of the playoffs, finished 19th in the NFL against the pass (241.6 ypg) despite having significant injuries in their secondary.
The Lions struggled defensively even though they invested heavily in the offseason.