CHARLOTTE, N.C. — Carolina Panthers safety Eric Reid knew something was up in the first half of Sunday’s 24-17 loss at Tampa Bay when a play was called in the defensive huddle that hadn’t been practiced all week.

“We were like, ‘Whoa!'” Reid said. “They told us [coach Ron Rivera] had called that play.”

On Monday, there was no doubt something was up. Rivera announced he was taking over the defensive playcalling the rest of the season from coordinator Eric Washington and fired two defensive assistants.

It was an effort to salvage a season — the Panthers are 6-6 after a 6-2 start — with four straight losses heading into Sunday’s game at Cleveland (1 p.m. ET, Fox).

Which begs the question: What kind of a playcaller is Rivera, who was a defensive coordinator at San Diego (2008-10) and Chicago (2004-06) before Carolina hired him as a head coach in 2011?

“I would say very instinctive,” said Hall of Fame linebacker Brian Urlacher, who played three seasons (2004-06) under Rivera with the Chicago Bears. “He was aggressive, too.

“He’s really good at putting guys in the right place. He’ll figure out what they’re good at and do more of that, what guys are comfortable with.”

The 2005 Bears were first in the league in points allowed with an average of 12.6 a game. The ’06 unit ranked third at 15.9 points allowed per game. Rivera’s 2010 unit at San Diego led the NFL in total defense, giving up 271.6 yards a game.

“When he was at Chicago, we ran two or three or four defenses a game and we played them well,” Urlacher said. “We played them fast and didn’t make mistakes.”

That’s what Rivera created at San Diego, where he cut out 45-50 percent of the playbook in an attempt to simplify. That’s what he’ll try to do the final four weeks at Carolina for a unit that ranks 14th in total defense after being a top-10 unit five of the past six seasons.

“You try to look at what you think fits and what they do well,” Rivera said. “The worst thing a player can do is think. Then the tendency is hesitate.”

The play Reid cited is Rivera’s instinctive side showing through. He had a feeling the call would work based on what Tampa Bay was doing and how his unit ran the plan in previous games.

“He uses the aggressiveness in a very calculated way, and I think all the good ones do it that way,” Browns coach Gregg Williams said as he described Rivera as a playcaller.

Williams and his staff studied what Rivera did as a coordinator to prepare for what they might see differently this week.

“He fits the scheme around the players, but doesn’t make the players be forced into a scheme they can’t do,” Williams said.

Baltimore safety Eric Weddle, who played for Rivera at San Diego, called Rivera “detailed and innovative.”

“He’ll do some different things to fix what’s not working,” he said.

The Panthers have struggled the most at consistently pressuring the quarterback and getting off the field on third down, ranking 23rd in sacks per pass play as well as 23rd in third-down efficiency.

With Rivera calling plays on Sunday, the Panthers had four sacks after having only four the previous three games combined. They were 4-for-4 in third-down efficiency in the fourth quarter.

Rivera, who played linebacker for nine seasons for the Bears, hopes the change has gotten players’ attention.

“It’s no different than when the owner comes around,” he said of having the head coach more involved in practice and playcalling. “Everybody picks it up a little bit.”

That Rivera already has the respect of players helps.

“As a player you can relate to him,” Urlacher said. “He makes you feel comfortable and he can relate to you. He puts you at ease with the way he handles you.”

Reid liked the way Rivera presented the game plan for the Browns.

“He likes to explain why we’re doing things, why he likes a call in a certain situation, the philosophy behind it, and then how to execute it,” he said.

Urlacher said that was a Rivera staple at Chicago: “We went out there every Sunday knowing exactly what we like to do and that makes it easier to play fast.”

Rivera admits there will be some adjustments. He won’t be able to “go after the referees verbally like I typically do,” because he has to be focused on the next defensive play. That happened once against Tampa Bay and Washington had to get the call in.

Rivera also will have to rely more on others for managing timeouts and challenging plays. Fortunately, he has Norv Turner, who was the head coach at San Diego while the two were there, as his offensive coordinator.

But Rivera still believes taking over the playcalling gives Carolina the best chance to win its final four games against Cleveland, New Orleans, Atlanta and New Orleans again.

“No one knows that defense better than he does,” Urlacher said. “I can see why he took the reins. He knows how to get players to make plays.”