In one of the surprise moves of the NFL off-season, the Carolina Panthers allowed All-Pro cornerback Josh Norman to walk away in free agency. Six months on, it looks like he took the team’s pass defense with him.

Through four games this season, Carolina’s pass defense efficiency has dropped more precipitously than any team since the 1970 AFL-NFL merger. One season ago, the Panthers posted a 15-1 record while ranking second in the NFL in yards allowed per pass play. Now, they enter Monday night’s game against Tampa Bay ranked...