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Jason Pierre-Paul slipped quietly through the Giants locker room after a walkthrough practice last week. He stopped at his corner locker, posed for some promotional photographs holding a newspaper announcing his NFC Defensive Player of the Week selection, then vanished as stealthily as he had arrived. No interviews. No brouhaha.

The Giants were on a six-game winning streak. JPP earned his Player of the Week award with three sacks and a snatch-and-score fumble recovery against the Browns. With 11 sacks in two weeks, the Giants pass rush was beating opponents almost single-handedly. It was time to coronate the 2016 Giants defensive line as rightful heirs to the 2007 and 2011 lines, the ones that propelled otherwise-unimpressive Giants teams to the Super Bowl and proved to be Tom Brady Kryptonite.

But JPP, less boisterous with the media this year than he was before the 2015 injury which cost him two fingers and the often-invasive coverage that followed it, would not be part of the festivities.

It turned out to be an omen. JPP suffered an injury early in a sloppy Giants loss to the Steelers. He underwent season-ending sports hernia surgery Wednesday. His charmed Comeback Player of the Year bid was over, and the Giants' hopes of riding their defensive front four to another shocking Super Bowl surge are in severe jeopardy.

The Giants suddenly need a miracle just to hang with the Cowboys on Sunday night, let alone make any noise if and when they reach the postseason. But Giants defensive lines have a long history of overcoming long odds and turning doubters into believers.

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Glue and Snowballs

Damon "Big Snacks" Harrison began his Giants career as a Pierre-Paul skeptic. "I was one of the ones who wanted to wait and see myself," Harrison said of his initial feelings toward JPP.

Everything about this Giants defensive line, from the start of free agency through the first month of the season, invited skepticism. Having finished last in the NFL in yards allowed in 2015, the team re-signed JPP to a one-year contract with almost $10 million in guarantees, even though he provided just one sack in half a season in 2015. They then dropped a five-year, $24 million guaranteed deal on Harrison and a whopping $40 million guaranteed contract on edge-rusher Olivier Vernon. It was a risky trio of expenditures with high backfire potential for a normally frugal organization.

Long before the pricey line began paying dividends, Harrison became a JPP believer. "From the very first day I met him, he didn't let the injury or anything else affect him," Harrison said last week. "He's proven everybody to be wrong."

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"He's throwing linemen around out there with the hand, too, if you're watching," Harrison added before the injury. Indeed, JPP's confidence in his damaged hand—ripping away from defenders, elevating to deflect passes, swiping fumbles before they hit the ground—was a major part of his resurgence and a catalyst for much of what the Giants line has accomplished.

But if JPP's bounce-back was the Giants' biggest surprise, Harrison may have been their biggest revelation, as well as their wisest investment. And now he must replace Pierre-Paul as a leader and tone-setter, if not a sack-generator.

"He's been a key component to the way this thing has jelled together," defensive coordinator Steve Spagnuolo said of Harrison. "And I'm not talking about when he's out on the field as much as when he's off the field.

"He's been the glue. He's been the guy who can get guys to refocus. You need somebody in the group who can do that, and he's been that guy."

Oddly enough, Spagnuolo wasn't expecting a team leader when the Giants signed Harrison. "I didn't know him as a person," he said. "We had an idea of the type of person he was. But we really just saw what was on film and hoped for the best on the other things."

The Giants discovered they had both a positive locker room presence and an interior defender capable of transitioning smoothly from a 3-4 defense to their 4-3 scheme. Pro Bowl-bound second-year safety Landon Collins went so far as to call Snacks the Giants' defensive MVP. "It's a lie," Snacks quipped when told of Collins' remark.

Vernon offered a more measured assessment of Snacks' impact. "It's a chain reaction," he said. "A snowball effect. What he does helps the linebackers, and so on."

That snowball did not start rolling, though, until midway through the season. The Giants recorded four measly sacks in their first five games. It looked like they squandered $75 million on a guy with a permanent injury, a tackle they knew little about and the third-most heralded player on the Dolphins defensive line.

But the Giants went on to record 23 sacks in their next seven games, with the pass rush often taking over late in games and sometimes bailing the inconsistent offense out. That '07/'11 vibe was back, and though the Giants weren't Super Bowl favorites by a long shot, their defensive line looked like an equalizer that could drag even the best opponents into an alley fight.

Now they must prove they can do it against their toughest opponent without their most dangerous player.

Trust and Repetition

While sacks were few and far between, the Giants line has been applying pressure since the start of the season. Pro Football Focus credited the four starters with a respectable 39 hurries in their first five games. Watch the early-season film and you will see Vernon and JPP frequently beating their blockers while Snacks and Johnathan Hankins, the one fully healthy holdover from last season, push the pocket. They just couldn't quite seal the deal.

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That changed when the Giants stopped playing like four individuals and began operating as a unit. "It's just locking in and trusting that the guy next to you is gonna do the job," Hankins said.

Harrison agreed. "Guys are used to playing with each other," he said. "We had the offseason, but it's not the same as actual game action."

Vernon also concurred. "It's just repetition, getting to learn about your teammates when you're out there," he said. "When you're on the field and it's live, you get a feel for everything."

A skeptic would point out that the Giants sack totals were low when facing the Cowboys, Redskins, Saints and Packers—teams with either great offensive lines, quarterbacks who know how to avoid sacks or both. The sack surge came against opponents like the Bears and Browns. The Giants recorded just two sacks against the Steelers last week, both acts of Vernon heroism. JPP was hurt for most of the game and Hankins limited for part of it, but a solid Steelers line and the savvy Ben Roethlisberger made the Giants line look mortal early in the game, when it was at full strength.

But there is more to the "chemistry and repetition" angle than a strength-of-schedule mirage.

"It took me, [Michael Strahan] and Osi [Umenyiora] a couple of turns to figure out where our strengths were playing with each other," Justin Tuck told Patricia Traina of FanSided before his induction into the team's Ring of Honor in November. "We knew our strengths individually, but when you throw that much talent on the field at the same time, you have to figure out how to add those together and not be subtractions."

Once Tuck, Strahan, Umenyiora and Mathias Kiwanuka jelled in 2007, they led the Giants to 53 sacks and an unexpected Super Bowl run. The 2016 Giants appeared to be trending in the same direction.

In the wake of JPP's injury, Vernon, Harrison and Hankins are going to need more than talent, trust and chemistry to do what their predecessors did. But then, no one gave those old Giants teams much of a chance, either.

Big Guys and Skinny Chances

Ben Roethlisberger noted the similarity between the current Giants line and the great ones of the recent past before last Sunday's game.

"That's where it starts with them: the way they get after the passer," Roethlisberger said. "Whether its Vernon or JPP, the edge rush, speed rush, power rush. And then you've got Jonathan and Harrison in the middle creating just all kinds of havoc."

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"That's what they had back in the [Super Bowl seasons]. They got the edge rush, with Strahan and those guys coming off the edge and creating havoc. But then they were stout enough up the middle in the run game or in pushing the pocket."

For Hankins, such comparisons were purely superficial. "We're totally different," he said. "We don't have four or five ends who can rush like they did. We have more big guys than skinny guys."

That lack of "skinny guys" is the Giants' biggest problem on defense right now. There's no depth behind Pierre-Paul. Head coach Ben McAdoo stressed what he called an "all hands on deck" approach to replacing JPP several times Wednesday.

Kerry Wynn is expected to start in JPP's absence, just as he did for the first seven games of last season. Wynn is a hustling, high-effort role player who has recorded two sacks in three seasons. Situational backup Owa Odighizuwa, still looking for his first career sack after two seasons, will see increased playing time. And rookie Romeo Okwara, sackless through 12 games of limited playing time, will also play a role, though he may be needed inside Sunday with Hankins also banged up.

The '07 Giants were so loaded with pass-rushers that Spagnuolo had to get creative about finding playing time for all of them. The 2011 team got 16.5 sacks from a second-year Pierre-Paul when Tuck and Umenyiora were sidelined for portions of the year. But this year's edition has relied on Vernon and JPP to play nearly every meaningful snap for much of the season. As so often happens in the NFL, lack of depth became a problem at the worst possible time.

"We got guys behind him who I believe are going to do a really good job,'' linebacker Jonathan Casillas said Tuesday. "But no one's Jason Pierre-Paul. No one can really do the things that he can do for us or for anybody.''

Hope lies with the big guys, and with Spagnuolo's creativity. Hankins has been quiet for much of the season, but he recorded seven sacks in 2014. He's the one who strip-sacked Josh McCown two weeks ago so JPP could run to glory. Spagnuolo slid Hankins to the outside in some packages before the Pierre-Paul injury, where the 320-pounder caused surprising size-speed problems for blockers expecting Vernon. "I can handle it out there for a couple of plays," Hankins said. "Whenever I'm out there on the edge, I think I'm pretty good out there."

Vernon, meanwhile, continued the long tradition of Giants outside pass-rushers by sliding inside on some third downs, sometimes with linebacker Devon Kennard shifting to defensive end the way Kiwanuka often did in the glory days.

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"I try not to get used to it too much," Vernon joked about getting banged around on the interior. "It's something I did at times in Miami. I'm comfortable with it."

And then there's Harrison, the quintessential 350-pound "big guy," who has recorded just three sacks in 60 career starts. Harrison's primary jobs are to stuff the run, an important duty against the run-heavy Cowboys, and occupying double-teams—crucial if Vernon ever hopes to face just a single blocker for the rest of the year.

Snacks is ready for an increased role. Sort of. "I'm gettin' old, man," he joked. "I used to like the double-teams. Now I try to run away from them. I try to pass them on to Hankins, a young guy.

"But it really helps make the team better," he said. "It causes other guys to make plays. I try to punch through the double-team and still make the play. Double-team or single-team, I still wanna make the play."

With JPP gone and the playoffs hanging in the balance, everyone must make plays.

Tests and Resilience

The '07 Giants operated all season in the shadows of a Cowboys team that finished 13-3. Then they beat them in the playoffs, en route to shocking a Patriots team that won 16 games and cast an even longer shadow.

The '11 Giants finished the regular season 9-7 and squeaked into the postseason. Then they beat the 15-1 Packers in the playoffs with four sacks and four turnovers before winning a rematch with the Patriots. But frankly, the '11 Giants never looked like a Super Bowl team until the moment Eli Manning hoisted the Lombardi Trophy. Even the defensive line paled in comparison to the '07 line.

This year's Giants actually looked better than their Super Bowl counterparts did entering December. That's what made Sunday's loss and the JPP injury so frustrating. The storyline for Sunday's Cowboys game looked preordained. Great offensive line versus great defensive line. Heavy favorite versus a Giants team with a longstanding reputation as giant-killers.

But Sunday night's game now looks like a mismatch. The Giants' playoff hopes are also cloudy.

Still, the Giants have the chemistry between the intense, explosive Vernon, the steady Hankins and chain-reaction-causing Snacks to fall back on. They also have Collins and an improving secondary, plus an offense with enough talent to hold up its end of the bargain if it gets its act together.

If a Giants December playoff push were easy or anticipated, it just wouldn't be a Giants December playoff push.

"We get tested in certain situations," Vernon said. "Sometimes we're resilient. Sometimes we give up some plays. But the main thing: We like to bend but not break."

The Giants aren't broken just yet. There's plenty of reason to be skeptical of them. But that has been the case since the beginning.

Mike Tanier covers the NFL for Bleacher Report. Follow him on Twitter @MikeTanier.