If the Eagles are going to be successful this season, and not merely interesting in a lab experiment kind of way, the most valuable player on the football team may be Connor Barwin.

Assuming the offense can score points as expected in Chip Kelly's frenetic manner, then it will be up to the defense to actually come through and not give the games back to the other teams. For that to happen, the newly installed 3-4 defense has to function properly, particularly in the base defense, when the outside linebackers have to be able to cover pass receivers.

When you make the list of Eagles outside linebackers who can do that consistently, it takes only one line to write them all down: Connor Barwin.

That seems like a bit of an oversight on the part of Kelly and the player-personnel department, but if there was any doubt they are light at that position, the final roster cut last weekend made it clear.

"Right now at our outside-linebacker spot, we have a lot of rush guys and not a lot of drop guys," Kelly said Wednesday when he reviewed his cutdown strategy and explained why he kept five inside linebackers and only three on the outside.

It made no sense to him to keep a fourth outside linebacker - a Chris McCoy or a Travis Long - if he couldn't do anything better than either Trent Cole or Brandon Graham and wasn't as useful on special teams as inside- linebacker reserves Jake Knott, Casey Matthews, and, now, Najee Goode.

"The one drop guy we had was Connor Barwin," Kelly said, just in case anyone missed the point.

"He said that?" Barwin asked.

He did. It isn't as if Cole, the starter at the other outside position, and Graham haven't been working to improve their skills in coverage, but both are defensive ends and it's not an easy transition. The extent to which offensive coordinators can figure out a way to take advantage of that will say a lot about the success of the defense, and that of the team as a whole. Offenses might play backward against the Eagles, running in passing situations and passing in running situations to get the matchups they want. Barwin makes that a lot tougher for them.

"It can get really complex," Barwin said. "We can do all kinds of stuff with the nickel and the safeties, and move me to left or right. It's just a versatility thing that I can rush and can drop. Those other guys, Cole and BG, are definitely capable of dropping. There are coverages they can do and you put them in the best situation to succeed."

Anything aside from a standard flat drop is probably not recommended, though, but it's the kind of thing Barwin has been doing for quite a while. Which is why he is so valuable. He can play zone, he can play man, he can put his hand in the dirt and rush the quarterback. Versatile? This is a guy who played in the Big East basketball tournament in Madison Square Garden for the University of Cincinnati.

"I've gone through this change before and it was very successful," said Barwin, who was converted to a 3-4 linebacker by the Houston Texans two seasons ago. "We plan to do the same thing here."

Barwin, in his fifth NFL season, was signed as a free agent in the spring. He lives downtown and likes walking the Rittenhouse Square and Fitler Square neighborhoods in the free time he gets. When he played for the Texans, he was considered a curiosity among his teammates because he often took public transportation and biked to practice, and, when he drove, it was a Prius hybrid dwarfed amid the monster pickups and Escalade RVs in the parking lot.

Barwin hasn't taken the Broad Street Subway to work here yet - "I take it to Phillies games, though" - but he's not ruling it out, either. And his wheels at the moment are attached to an all-electric Tesla.

In other words, he's unique, and not just because he's the only Eagles linebacker who can reliably cover a receiver. That's the part that might make him the most valuable player on the team, though, at least when it comes to making the 3-4 work.

If anything were to happen to Barwin, the Eagles are in real trouble. Casey Matthews is being schooled on playing the outside in a pinch. Kelly calls it "cross-training," but there are some other words for that as well.

"You better have some versatility," Kelly said. "So if somebody like Connor were going to go down, you better have another drop guy."

The problem is they don't, although it's not a problem quite yet. It won't matter until the offensive coordinators in the NFL start probing the Eagles defense and find the weak spots. Then the problem will be that they don't have two Connor Barwins.

For the moment, at least they have one of them, and he's doing everything he can to make sure that will be enough.