No. 1 reason to believe in Bears in 2016? Vic Fangio and Co.

BOURBONNAIS — Linebacker Danny Trevathan didn’t miss defensive coordinator Vic Fangio’s dance, or whatever that was when Fangio picked up a flag to celebrate a negated touchdown during some fierce goal-line work that concluded practice Thursday.

“That just means that he’s out there with us,” Trevathan said. “He’s having fun calling plays. And we can sense it.”

If Sundays turn into dancing days for Bears fans, it will be because of Fangio and his highly respected defensive staff. They are the closest thing to a sure thing the Bears have after a change at offensive coordinator and an influx of youth.

“We have a chance to be a better defense than we were last year, but the proof will be in the pudding,” Fangio said. “Practice is the quiz, the games are the final exam. So until we start playing and see exactly what we’ve got, that will determine the true answer to that question. But we have a chance to be better.”

The chances to improve begin with the new faces: Trevathan, inside linebacker Jerrell Freeman and defensive end Akiem Hicks. They include improvements from defensive tackle Eddie Goldman and safety Adrian Amos in their second seasons as starters. And they involve having outside linebackers Willie Young and Lamarr Houston healthy since the start of the offseason program.

Fangio has been dealt a much better hand than he was given a year ago. But he insists he’s still unsure of how it will work out.

Last year, Fangio said he scaled back his defense because he was limited by his players’ talents and experience. He said he has seen some signs that his current group can handle more, but he hasn’t installed more schematically since the spring.

Why?

“These first few weeks of training camp are all about fundamentals and techniques,” Fangio said. “So when we lay the foundation for that and we see where we are, then we’ll see if we can start graduating from Algebra 1 to Calculus and schematically.

“We’ll see. We’ve got veteran guys, but they’re not veteran in our system yet.”

In other words, he’s still getting a sense for what his players can and can’t do. That includes Trevathan, who received the richest free-agent contract this year from the Bears to be one of the faces of Fangio’s defense.

“I’m going to be all over the field,” Trevathan said. “That’s kind of what I see.”

But Trevathan knows he hasn’t seen everything. He knows that Fangio has more to install — if he thinks the players can handle it.

“Once we get out here and we learn more plays, we can really turn that swag on and go play ball,” Trevathan said.

History says that Fangio will figure it out. Forget his success in San Francisco. Just look at what his defense did last season. There were positives, regardless of the Bears’ 6-10 record.

Despite shortcomings in personnel, the unit ranked in the top 10 in total defense from Weeks 2 to 10.

Despite starting two rookie safeties in four games last season, the defense finished fourth against the pass.

With Shea McClellin as the primary signal-caller, Fangio’s defense ruined “Brett Favre Night” at Lambeau Field by harassing and frustrating quarterback Aaron Rodgers into arguably his worst performance last season (62.4 passer rating, 51.2 completion percentage).

If Fangio can make something out of McClellin, he undoubtedly can find ways to incorporate rookie outside linebacker Leonard Floyd’s speed and athleticism into actual production.

“He’s a mastermind,” Trevathan said. “He’s just doing a good job of feeling his players and knowing what they’re good at and putting you in situations to make plays.”

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Email: ajahns@suntimes.com