"Bad," Rivera said Monday. "There's no other word for it."
Panthers defensive coordinator Steve Wilks counted 12 missed tackles in all - by far a season high for the league's No. 2-ranked defense coming into the game.
Carolina (8-4) allowed 400 yards to Drew Brees and the Saints, dropping them to No. 6 overall in the NFL. More importantly, the Panthers fell one game behind the Saints (9-3) in the NFC South, which might as well be two games given New Orleans swept the season series and holds the head-to-head tiebreaker.
The Panthers were short-handed on Sunday with outside linebacker Thomas Davis limited to 39 percent of the snaps due to a hamstring injury and defensive end Charles Johnson out serving a four-game suspension for violating the NFL policy on performance enhancing substances.
Wilks, who took over as coordinator this season after Sean McDermott left to become head coach of the Buffalo Bills, called the effort "unacceptable" and vowed the tackling problem will get fixed this week.
Wilks said it's a "misconception" that players can't work on tackling during the season because of the limits placed on teams as part of the NFL's collective bargaining agreement.
"The tackling part, to me, is not a physical thing. Every guy in that room right there, they're physical. They have those attributes or they wouldn't be in that room," Wilks said. "To me it is an emphasis on detailing your work. ... You have to get into position where you are ready to tag off each and every time, understanding where you help is and trying to leverage the football."
Rivera pointed to plays where players failed to wrap up and lost control of their games against Saints running backs Alvin Kamara and Mark Ingram. The duo ran for 145 yards and three touchdowns on Sunday, including a 72-yard burst by Ingram that broke the game open.
"Part of (missing a tackle) is the result of not being where you're supposed to be," Rivera said. "Part of it can be a guy can get downhill to his crease and instead of keeping that gap constricted, he works sideways - which you don't want to do because it makes that gap bigger."
Rivera said that often led to a bigger area for the next defender to cover and resulted in more arm tackles and fewer shoulder tackles.
"It happens," safety Mike Adams said of the poor tackling. "We will get that fixed though. We just have to do our job across the board, everybody. ... We just have got to play better as a whole. A mistake on this play and on that play doesn't help us at all."
The good news for the Panthers is they play their next three games at home, beginning Sunday against the Minnesota Vikings (10-2). Then they host Tampa Bay and Green Bay before closing the regular season on the road against Atlanta on Dec. 31.
"We have got to win them all," said linebacker Luke Kuechly. "I think that that's the biggest thing. ... We have our work cut out for us, but we are excited to be at home in front of our fans. They give us a lot of good energy."
NOTES: Rivera believes the team will have a better chance of getting tight end Greg Olsen back this week since the game will be on natural grass, rather than an artificial surface.
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