CHARLOTTE — Panthers coach Ron Rivera learned a valuable lesson when he took over defensive play-calling duties midway through last season: You can't afford to be predictable in today's NFL.

That's why Rivera is mixing in a three-man defensive front — along with a few other surprises — to go along with the base 4-3 defensive scheme the Panthers have used the last eight seasons.

"The biggest thing is that we are playing so many multiple style offenses that you just can't line up and let them attack you," said Rivera, who previously spent six seasons as a defensive coordinator with the Chicago Bears and San Diego Chargers.

That's one reason Carolina drafted Brian Burns in the first round and Christian Miller in the fourth, and why they signed free agent Bruce Irvin — all speed edge rushers who have the flexibility to drop into coverage.

And earlier this week, the Panthers signed three-time All-Pro defensive tackle Gerald McCoy to a one-year deal. McCoy, 31, has been one of the better players at his position over the last nine seasons with the Tampa Bay Buccaneers, and is the only NFL defensive tackle with at least six sacks in each of the last six seasons.

The Panthers have regularly been a top 10 defense, which led to them losing defensive coordinators Sean McDermott and Steve Wilks to head coaching jobs elsewhere. Last year Carolina promoted Eric Washington as its third defensive coordinator in three seasons, but when things began to fall apart on that side of the ball Rivera stepped in to assume play-calling duties.

"In the middle of the year I started doing some different things, and I saw that every time we did some of those things positive things happened," Rivera said.

That included disguising blitzes, dropping defensive linemen into coverage and mixing up defensive fronts, among other tweaks.

The problem was the Panthers didn't have the personnel to do all of the things Rivera wanted to do, which is why general manager Marty Hurney sought out adding versatile edge rushers.

Burns, in particular, is viewed as an integral part of the team's future in this new more diverse defensive scheme.

"It makes the defense more versatile and I come from a school that did it all of the time," said Burns, who played at Florida State. "We played a 4-3, a 3-4 and a whole bunch of other packages, so I'm used to rushing the passer and dropping" into coverage.

He's also familiar with the lingo involved, which should allow him to play more freely and without overthinking things.

"Just being able to do both, no offense can really scheme me or know when I am coming at any particularly play," Burns said. "I can disguise as if I'm dropping and really come off the edge and that can free up me or other people."

When the Panthers go to a 3-4 front look for two-time Pro Bowl defensive tackle Kawann Short to slide out to defensive end.

The Panthers are still in the early stages of installing their new defensive looks, but Rivera has been pleased by the team's retention.

Now, he said, it's a matter of time to see how much of what the team is installing can be effectively used this season.

"It's neat to see the things you are capable of doing, but we won't know (how much) until we get into the preseason or regular season," Rivera said.

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