CHARLOTTE, N.C. -- Ron Rivera hasn't gone to work during any season feeling as if he might be fired ever since a 1-3 start in 2013, because former Carolina Panthers owner Jerry Richardson made it clear then that wasn't his intention.

"He's always told me he would make no decisions until after. So I've always had that [assurance]," Rivera revealed in 2015 when the Panthers were making a run to Super Bowl 50. "And I've never used that. He told me if I ever had to I could tell that to you guys and I never did.

"And I appreciated that because it gave me comfort and solace going forward that I could do my job, work as hard as I could, do the best I can and at the end of the day he'll evaluate me."

Rivera gave no indication on Monday he has the same assurance from new owner David Tepper.

His staff certainly doesn't.

Rivera fired defensive line coach Brady Hoke, secondary coach Jeff Imamura and announced he was taking over the playcalling duties from defensive coordinator Eric Washington following a fourth straight loss that left the Panthers at 6-6.

It was the first time Rivera fired a coach during the season since Richardson told him he didn't have to come to work looking over his shoulder. His only in-season firing since being named Carolina's head coach in 2011 came in 2012 when he let go of special teams coach Brian Murphy.

So Monday's changes speak volumes.

Rivera said Tepper didn't influence his decision to make staff changes. But Rivera obviously felt pressure to make the changes now instead of waiting until after the next four games in an attempt to salvage the season.

And perhaps his own job.

"Right now no one is exempt, even myself," said safety Mike Adams, the only defensive player willing to discuss the changes and what they meant during Monday's open locker-room period. "I play every day like my job is on the line. I know he coaches every day like his job is on the line. I've seen Peyton Manning get cut, Champ Bailey get cut, so nothing surprises me anymore. No one is exempt."

One could argue Rivera didn't make these changes soon enough, before it got to the point of desperation that exists now with Carolina basically needing to win out to make the playoffs.

The defense has underperformed most of the season while the offense, for the most part, has exceeded expectations under new coordinator Norv Turner.

The defense ranks 27th in the league in efficiency after ranking 10th, 10th and 2nd the past three years, according to ESPN Stats & Information. Defensive efficiency is calculated by taking a team's success on a per-play basis and scaling it 1-100.

As good as Carolina is in some categories -- according to ESPN's pass rush metrics using NFL Next Gen stats, the Panthers are first in beating their blocks by 2.5 seconds, doing so on 62 percent of their rushes -- they are bad in others.

None speaks volumes more than pressuring the quarterback and third-down efficiency. The Panthers are tied for 19th in sacks with 29 after finishing the past two seasons ranked third (50) and second (47) in sacks.

That's helped opposing quarterbacks compile a 62.2 Total QBR compared to 51.7 a year ago.

The Panthers rank 23rd in third-down defensive efficiency with a rating of 40.43 percent. They were 12th a year ago at 37.38 percent.

The results were better on Sunday after Rivera took over calling the plays on defense. The Panthers had four sacks after having only four the past three games combined. They still struggled on third down, giving up six on 13 (46 percent) tries, but several of those came on penalties.

Rivera hopes his presence calling plays as he did as the defensive coordinator in Chicago (2004-06) and San Diego (2008-10) will help turn things around. The Bears had the second-best defense in the NFL in 2005.

San Diego had the league's top-ranked pass defense in 2010 and ranked 10th in total defense, helping Rivera land the Carolina job.

"It's an opportunity for me to work even closer with [Washington] to help him out as we go forward," Rivera said. "Y'all got to remember your first time doing something. You weren't perfect and somebody had to help you. That's really what I'm here for."

Rivera admitted the turnover in defensive coordinators the past three years "to a degree" has caught up with the team. Sean McDermott left for Buffalo after the 2016 season and Steve Wilks for Arizona after last season.

"It's been trying, obviously, when you lose guys that have been in this system for a long time," Rivera said. "As we move forward, it's about learning and growing and getting back to where we've been in the past, especially as a defense."

That the Panthers didn't play to expectations has been frustrating for veteran players such as Adams.

"At the end of the day coaches put us in good positon by making calls, [but] third-and-15, we can't let a ball go over our head. Third-and-17, fourth-and-3, we've got to get off the field," Adams said. "That's on us as a defense. We can't put that on the coaches. ... We should have gotten it done and put the coaches in a better position."

Failing to do so put the pressure on Rivera to make in-season changes that he typically wouldn't. Awareness is heightened that the person beside you may not be there tomorrow.

"Your antennae has got to be up," Adams said. "Everyone's job is on the line every time we go out there."

But amazingly morale hasn't hit rock bottom because the Panthers still have an outside chance at the playoffs. They still are in the hunt for a wild-card spot with Seattle (7-5), Washington (6-6) and Minnesota (6-5-1) and Philadelphia (6-6).

The issue is that it likely would take four wins -- with two of those games against New Orleans (10-2) -- to make the playoffs.

"It's crazy because we still have a chance," Adams said. "We still have faith. We still believe we can go out and start ripping off some wins.

"We lost four in a row. Why can't we win four in a row?"

The NFL is full of anything-can-happen scenarios that have come to fruition in the past. The Panthers won their final four games in 2014 to win the NFC South and make the playoffs with a 7-8-1 record.

To do it now, though, everyone will have to do their job while looking over their shoulders.