Paul Worrilow’s long-shot breakthrough into the NFL has been a bittersweet one.

Over the past two seasons, the hard-charging undrafted linebacker from Delaware emerged as the Falcons leading tackler. But he’s been on two losing defenses and a unit that finished last season ranked last in the league.

After making 12 of 16 starts and taking 137 ball carriers to the ground as a rookie, Worrilow started all 16 games last year and led the Falcons with 155 tackles.

But under new head coach Dan Quinn, Worrilow, who’s draw early praise, is hoping to put those seasons behind him.

“We are focused on what’s in front of us,” Worrilow said. “The past, that doesn’t exist for this group anymore. It’s a whole new group, a whole new defense. It’s time to invest in today and what we can do to be the best defense out there.”

The Falcons are retooling the linebacker corps. They signed free agents Brooks Reed, Justin Durant, Allen Bradford and linebacker/defensive end O’Brian Schofield. Reed, who’s battling a hip strain, and Durant appear set to replace Joplo Bartu and the departed Sean Weatherspoon at strongside and weakside linebacker.

Other linebackers in training camp include Nate Stupar, Marquis Spruill, Boris Anyama and Derek Akunne.

Worrilow, who was challenged to improve his mobility during the offseason, remains as the No. 1 middle linebacker.

“Paul is one of the guys that really defines grit,” Quinn said. “He just won’t back off.”

Worrilow was the team’s signal-caller last season and will likely retain that role. Last season, he had to relay the dizzying number of calls from former defensive coordinator Mike Nolan and the defense never took shape or formed a personality.

Quinn, who’s likely going to be the play-caller, has a KISS (keep-it-simple-stupid) approach. While Quinn has been fostering competition, Worrilow is headed for the starting lineup.

“When you go and see him and the communication that he has, he’s always trying to improve,” Quinn said. “That part of his game. You can see it all the time. He’s very critical of himself, but at the same time, he’s really developing into a leader as well.”

Worrilow has made it a point to hit it off with newcomers Reed and Durant.

“We are getting to know each other on and off the field,” said Durant, who played with Dallas last season. “We talk about different stuff. It’s not all about football all of the time. … He’s a real good dude, real cool and he’s funny.”

Durant and Worrilow believe that relationship will carry over to the field when the Falcons are trying to stop Philadelphia and coach Chip Kelly’s potent offense in the season opener on Sept. 14.

“We have to establish one (relationship) off the field first and then bring it to the field,” Durant said. “We are playing well together.”

Worrilow said he is looking forward to the defense coming together in the first exhibition game against the visiting Titans on Aug. 14.

“Not just competing, which is always what we are out there to do, but with our fellow teammates forming that group, that core, that love for each other,” Worrilow said. “That’s super important when it comes to playing on Sundays.”

The Falcons could have as many as six new starters on defense and possibly a couple more in the nickel defense.

“It’s going to come down to the players,” Worrilow said. “You can have whoever out there, but you’ve got to have the attitude and the effort. We have to go out there and play Falcons defense.”

A Falcons defense that Worrilow wants people to be proud off.