BENNIE LOGAN'S rookie contract expires after this season. Unless the Eagles extend his contract, he can become a free agent. So: What is Logan is worth? Unlike other positions, run-stuffing defensive tackle can be a difficult spot to quantify.

One simple metric: The Eagles are 4-1 when Logan is playing and healthy, 1-3 when he is not.

It seems unlikely that the club would use an exorbitant franchise tag on Logan, who is not, by any stretch of the imagination, a franchise player. He is, however, 6 feet, 2 inches and 315 pounds of in-his-prime disruption. He is the sort of player whose presence makes the job of the other front-seven players easier. He is not irreplaceable, nor unstoppable; but, he is virtually unquantifiable.

The Giants snagged Damon Harrison in March with a five-year, $46.25 million deal with $24 million guaranteed. Harrison had 193 tackles and 1 1/2 sacks in his three seasons with the Jets. Logan, in his fourth season with the Eagles, had 171 tackles and three sacks in his first three seasons. But the Giants were desperate to improve their defense. Is Logan worth as much as Harrison? More? Less?

"We have great chemistry and it would be great to have him here," said Cox, "but you live in the moment. That's the business side of the NFL."

Harrison and Logan operate in close quarters, part sumo wrestler, part judo master; every play, seeking to upset the offense's plans from the middle of the field.

"Disruption is a part of those guys' job description," said defensive coordinator Jim Schwartz. "They're not holding blockers off and trying to free other people up to make plays. They're trying to disrupt things. If we can get tackles for losses, that helps us win drives. You take teams and put them off schedule, second-and-long, third-and-long."

Logan is putting teams off schedule time after time. The Eagles probably will keep Logan in every type of green for the foreseeable future, though he says he won't worry about it until he has to.

"They came to us a little in the offseason," Logan said, "but I don't even think about that stuff while the season's going on."

He's got plenty on his plate.

Last winter the Eagles abandoned Chip Kelly's affinity for free-agent mercenaries and returned to their form with an orgy of in-house spending that retained many of Logan's contemporaries: Cox, tight end Zach Ertz, defensive end Vinny Curry. They might have to cut or trade a couple of older players to make room under the salary cap for Logan, who will be 27 next season. The Eagles have never been shy about shedding popular, expensive players on the verge of losing a step, such as defensive end Connor Barwin, who is four years older than Logan, or left tackle Jason Peters, who will be 35.

Logan is plenty popular himself; a laconic Louisianan who has become everything Philadelphians adore. He's a selfless defensive player. He's a small-town guy who says, "I love this city." He attends the other teams' games - especially the Flyers, and even the Soul - and he always tweets his appreciation for their hospitality. One of eight kids, he is generous to a fault with a soft spot for the homeless. He would be a cop if he didn't play football.

But he does play football. He will only get better at it.

Logan enjoys a remarkable chemistry with Cox, Andy Reid's last first-round pick, in 2012. Logan came aboard in 2013, a third-round pick out of LSU in the first year of the failed, three-year Chip Kelly Experience. By the middle of 2013, Logan had replaced veteran free agent Isaac Sopoaga as the starter at nose tackle in the 3-4 scheme. By the end of 2015, he was considered a top-notch run stuffer. While he blossomed further when the Eagles hired coordinator Jim Schwartz and switched to a 4-3 attack, Logan actually increased his value by his absence.

The Eagles were 3-1 and tied with Washington late in the first half when Logan strained his groin. Washington proceeded to score 10 unanswered points. The Birds beat the Vikings the next week, but they needed to relentlessly blitz Minnesota's undermanned offensive line. Logan missed the next two games, and the Cowboys and Giants tagged the Birds with 29 and 28 points, respectively, the most points the stingy defense surrendered all year.

Logan returned against the Falcons on Sunday. Matt Ryan brought in the top-ranked offense in the league. It left with 15 points and a loss. Logan recorded zero tackles . . . but it was, nevertheless, a performance Logan can use in negotiations.

Schwartz noticed.

"Our run defense was good, and it has been good, and Bennie has been a part of that," Schwartz said. "It's put them in a lot of third-down-and-long situations, and it's allowed our defensive secondary to be able to cover, get off the field. We didn't get a lot of pressure, but I think stopping that run and putting them in some third-down-and-long situations had a lot to do with it, and Bennie is a big part of that."

Indeed he was.

On the Falcons' first possession, Logan beat guard Andy Levitre and nearly tackled Devonta Freeman for a 4-yard loss. Freeman was stopped for no gain. On the Falcons' third possession, Logan shot into the backfield past center Alex Mack and got a piece of Freeman, who was dropped for a 2-yard loss. Late in the first half, deep in Eagles territory, two blockers pounced on Logan, which left a giant hole for safety Malcolm Jenkins, who hit Freeman for a 2-yard loss. Finally, it was Logan wrapped around Matt Ryan's ankles when Ryan was flagged for intentional grounding, which led to a punt with less than 6 minutes to play.

It was a triumphant return.

"I played absolutely terrible," Logan said endearingly. "My technique was rusty. My pads got too high a few times. Terrible."

Really?

"No," Cox said, laughing. "It was nice to have him back. At times he was dominant."

That dominance was just hard to spot.

There's a reason why Schwartz said that if he had played in the NFL, he'd want to play like Graham, not Logan. Graham, like Cox, is a better player. They make the tackles for the big losses themselves. They bring down the quarterback.

They also are first-round picks in the midst of contracts worth a combined $128 million.

Logan will make $1.66 million this season. He has made a little more than $3 million in four seasons.

No matter what he ends up getting, he's worth a lot more than that.

hayesm@phillynews.com

@inkstainedretch Blog: ph.ly/DNL