The Green Bay Packers’ switch to the 4-3 single high safety defense under Jeff Hafley is a significant departure from the 3-4 2-gap quarters-style scheme they previously ran under Joe Barry. That scheme drew inspiration from Vic Fangio-style defensive schemes thanks in large part to Barry’s time with Brandon Staley. It was implemented at a time in the NFL when teams were starting to play more two-deep/quarters defenses to limit explosive pass plays the new wave of Shanahan offenses were creating.
Under Hafley, the goal is to play a more aggressive man coverage or zone match single-high safety defense that lets the defensive front “pin their ears back” and rush the passer (and fit the run) more aggressively in a 1-gap defense.