THE BIGGEST difference between the Eagles' 2012 defense and this one, the group that hasn't allowed more than 21 points in any of its last eight games, just might be Connor Barwin.

It's a little hard to isolate a single factor, when a team changes schemes, coordinators, cornerbacks, and other stuff, but, hey, the Eagles host the Lions on Sunday. Barwin is from the Detroit area, he has an outline of the Motor City skyline tattooed on the inside of his right biceps. Plus, defensive coordinator Bill Davis set the table for us nicely yesterday.

"Connor makes the scheme go," Davis said. "I move him around multiple spots. He's on the outside on the right, outside on the left, he's inside . . . The position is called the 'Jack'; the 'Jack of all trades' is what it was originally named. We move him around and we have different techniques we use with him, and he's great with picking them up; if I need an edge set on one side, or a certain reroute or chip, Connor is the guy we go to.

"He wears a lot of hats and doesn't get as many [pass] rushes as he would like, but does a lot of things for the defense . . . He would love to be rushing every down and getting more sacks, but he's dropping [into coverage] and doing more other things, and never says a word about it."

Barwin's duties in Sunday's 24-21 victory over the Arizona Cardinals frequently included jamming Larry Fitzgerald at the line. As usual, the linebacker was on the field for all 71 snaps, though he didn't register any of the Birds' five sacks of Carson Palmer, and was credited with only one solo tackle on the score sheet.

"If our guys are rushing, sometimes the best pass rush doesn't get the sack," Davis said. Davis was defending Trent Cole, but the point also applied to Barwin. "It gets the quarterback moved off the spot, and then the guy that might have had a horrible pass rush gets the sack."

Free agency, you might have heard by now, is not a panacea in the NFL. The best teams grow their own guys, within their systems, don't depend on grafting high-priced key pieces from other teams. It's an interdependent game, and it can be really hard to predict how someone will play in a new setting. (See the 2011 Eagles for several examples.) But Barwin has been everything management might have hoped after signing for 6 years and $36 million as the Eagles' top acquisition in last offseason's market.

"To have him come here, he was the perfect fit for us," said middle linebacker DeMeco Ryans, Barwin's Houston teammate before Ryans came to the Eagles in 2012. "He's the reason why we can do so many of the things we do."

Barwin said his duties here are "pretty different" from his role with the Texans.

"We ran a 3-4, but I set the edge on the run game and I rushed the passer, on third down or second-and-long. This is a lot different," he said. "It's been great. The defense is playing well . . . [Davis] is only asking me to do things that I'm capable of doing . . . He's letting the defense evolve with the type of players he has. He's calling the game because of the type of players he has. I think as the season's gone on, we've learned about him, he's learned about us, and the defense has kind of come together, with a little bit of everybody."

Center Jason Kelce used to get into fights with Barwin during Cincinnati Bearcats practices, Kelce said.

"We were always high-energy guys, very competitive," Kelce said. "Whenever something went wrong, tempers always flared . . . He was just one of those teammates you loved playing with."

When players talk about Barwin, they often talk about his athleticism.

"Connor's always been a freak, in terms of his physical ability," Kelce said. He recalled that when the Bearcats would break into position groups for running, Barwin, who had bulked up after switching from tight end to defensive end, would run with the defensive backs, just for fun.

"He used to run 350 meters, all the way around the football field, and he would finish in first place, and wouldn't get tired . . . The DBs weren't a fan of it, getting beat by a 270-pound guy," Kelce said.

Barwin grew up as one of four sons of a city manager, Tom Barwin, who then managed Hazel Park, Mich., and now manages Sarasota, Fla.

"I'm a city guy - I love where I live, I love the walkability," Barwin said.

The city has been as good a fit as the team, Barwin said. He lives near Rittenhouse Square, sometimes takes the bus, subway or his bike to work. A recent piece on the online journalism site Grantland chronicled Barwin's attendance at the Animal Collective show at Union Transfer.

"He's always been that person," Ryans said. "He used to ride a bike in Houston, drove an electric car," a Tesla, which Barwin still owns. It stands out, nestled among the F-350s and Escalades at NovaCare. "When I seen him doing it, I'm like, 'Man, that's something we should all be more conscious of, thinking about saving the environment.' He is an interesting person and a cool guy to be around."

Barwin played varsity basketball and, before switching positions, was Brent Celek's backup for two seasons at Cincinnati.

"He hasn't changed," Celek said. "He just dresses a little nicer, 'cuz he's got more money. But he's the same dude. I knew from the beginning that Connor would be a huge part of this defense - his personality, the type of leader he is . . . He's kind of a big-city guy, and he loves when people are passionate about things. Our fans are definitely passionate about this football team."

On Twitter: @LesBowen

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