Jim Schwartz groaned. The Eagles defensive coordinator was being asked about his picket-fence defense for the second time in training camp, and he had clearly grown tired of talking about a scheme he so rarely used.

For all the attention the scheme has gotten from reporters and fans, Schwartz has used the soft zone coverage for only 37 out of 3,288 plays over the last three seasons. That’s just a little more than 1 percent of the time.

The coverage has been a lightning rod of sorts because some have incorrectly lumped all of Schwartz’s soft zones under the picket-fence label. But it’s not the only scheme he calls on long third and fourth downs, although the numbers suggest that maybe he should call it more.

The Eagles are a perfect 37-for-37 in Schwartz’s sticks defense. They have yet to surrender a first down, although they twice allowed so many yards on third down that one opposing team converted on fourth down and another kicked a long field goal.

The numbers should be overwhelmingly in the Eagles’ favor. It’s difficult to convert a first down from 14 yards — the shortest distance Schwartz will typically employ the picket fence — and beyond. But in the 46 other instances when he’s called another coverage under similar circumstances, the Eagles have allowed eight conversions, including five last season alone.

It’s important to note that there are variables — such as field position, timing, and score — in which it doesn’t make sense to choose a coverage that could surrender 10-plus yards and still be deemed a success.

But there have been a few occasions — most notably, in the overtime loss to the Titans last season — when the picket fence might have produced the desired results.

It’s not always pretty. It can be too passive for some tastes. Schwartz’s defense actually got burned by Carson Wentz and the Eagles offense earlier this training camp. But it usually gets the job done.

“If you play with discipline, you tackle well, you rush well,” Schwartz said earlier this month, “that’s a tough combination when the offense is so far behind the sticks.”

Here’s a film breakdown of the coverage, how it works, why it works, how offenses attack it, and when it might have made more sense to use it:

The set-up

Schwartz first called the picket fence in his first game as Eagles defensive coordinator. Some call it a “sticks” defense because most of the defenders are lined up across the field at the sticks, anywhere from 1-5 yards in front of the first-down marker. In this example from 2016, the Browns faced third-and-20. The Eagles rushed four down linemen and kept seven in coverage with a deep safety just beyond the marker.

Most offensive coordinators will run some sort of screen against such odds, but a draw is also an option, and considering that Cleveland was backed up, it wanted positive yards and gained 11.

The responsibility of the seven deep defenders is fairly simple. Rally to the ball and tackle.

Schwartz: “I think it fits us. One thing about me, we don’t really care about how many yards we give up. It’s about getting off the field on third down and keeping points down. Whether you’re giving up 10 yards on the third-down-and-long play or playing good red-zone defense, it’s all just part of the same thing.”

Defending the screen

Whatever the coverage on third-and-plus-15, offenses often call screens. But there are usually more of them vs. the picket fence because of the cushion of space the defense allows.

Eagles safety Malcolm Jenkins: “You get everybody back at the sticks, and when teams try to check it down, it’s kickoff coverage for us. Everybody’s flying to the ball urgent trying to get him down before the sticks.”

On this third-and-17 in 2016, the Redskins had several blockers out in space and managed to pick up 15 yards. But they were still only at their own 32 and elected to punt on fourth-and-2.

Defending the downfield pass

Quarterbacks throw downfield rarely against the picket fence and at their own peril. In this game from 2017, the Cowboys faced third-and-17 from their own 18, trailing by 7-6. Dak Prescott threw to receiver Dez Bryant. The ball was underthrown, and cornerback Ronald Darby made the interception. But even if the ball had more air under it, Jenkins would have been there.

In practice earlier this month, Wentz connected with receiver Nelson Agholor on a similar route for a 35-yard gain.

Wentz: “Sometimes you want to try and throw it through a defense. … You’re not going to make a living taking those shots, but it’s something to stress the defense so they can get better here in camp and see what we can get away with.”

Jenkins wasn’t on the field, but new safety Andrew Sendejo was and he had yet to practice the coverage.

Jenkins: “Nelson just got down the seam. Our offense just tried to throw through it, and I think guys were caught flat-footed. … It was a really good throw, really good catch. It happens.”

Wentz: “You have to be pretty spot-on. Yeah, that was a good case of me and Nelson making a play and making them pay for it.”

Defending the scramble

Mobile quarterbacks offer a different set of challenges. If an offense can stretch the coverage with deeper routes, it could create room for a quarterback to scramble. The Panthers’ Cam Newton has the arm to test secondaries and the legs to scramble downfield. But on this third-and-15 from last season, 12 yards were all he could gain before linebacker Jordan Hicks knocked him out of bounds.

Just tackle

Tackling is always important, but more discipline is required in the open field. If a defender can make a stop on the first try, as cornerback Patrick Robinson did here two years ago, all the better.

But if there are missed tackles, there should be a swarm of other defenders to keep damage to a minimum. In this game two years ago, Chiefs receiver Albert Wilson made three Eagles miss, but he was still six yards short of a first down when a fourth defender finally got him down.

Jenkins: “We got everybody back with a visual on the quarterback. So we got most of the guys breaking on the ball. It’s just smart football. While you kind of hate giving up yards, at the end of the day, the goal for the defense is to get off the field.”

Pressuring the QB

Fans of the blitz aren’t necessarily fans of Schwartz. He’d rather rush only four. It’s one reason the Eagles invest significantly in their defensive line. If you can generate pressure with four, why send more? Those who live by the blitz are sometimes as likely to die by it. But there needs to be a change of pace, and Schwartz has blitzed a few times on third-and-long, although never in the picket fence.

Screens are tailor-made for the blitz, and why would you send more rushers when you’re likely to see a screen? And why when you have defensive linemen, such as Fletcher Cox, who are capable of winning up front, as he did here against the Bears two years ago?

Schwartz has experimented with different looks up front in the picket fence. He has stood two linemen up and let them roam behind the line. He also has spread the ends out wide, even farther then when they are nine-techniques.

In the second half of last season, Schwartz rushed three down linemen with a roving linebacker — typically Kamu Grugier-Hill — at the second level. It worked as well as any formation. Grugier-Hill was able to identify screens and snuff them out early, as he did here against the New York Giants.

Picket-fence failures

Last November, Schwartz called the picket fence on third-and-15 and the Cowboys picked up 14 yards with a screen pass. Even though they were on their own 40, they elected to go for it on fourth-and-1.

Schwartz: “I remember saying on the sideline, ‘Hey, is that the time that it finally …?’ — because I would include, if you gave up enough yards on third down that they went for it on fourth and converted, I would consider that as the defense being defeated.”

But the Cowboys were penalized for a false start on fourth down and punted.

Still, the Eagles had allowed a first down by Schwartz’s definition a year prior against the Panthers. Newton flicked a short pass on third-and-17 to running back Christian McCaffrey, who picked up 15 yards after Jenkins missed a tackle.

Jenkins was upset with cornerback Rasul Douglas after the play because he was supposed to drop. Otherwise, Jenkins might not have lunged at McCaffrey.

Carolina converted a fourth-and-2 on the next play, although Newton eventually tossed a rally-ending interception.

Schwartz didn’t mention if he considered allowing a field goal as a picket-fence loss, but it did occur against the Jaguars last year. Faced with third-and-21 at their own 46, quarterback Blake Bortles dumped a screen to running back T.J. Yeldon.

The Eagles’ pursuit was sloppy, and Yeldon picked up 15 yards just before halftime, enough for Jacksonville to attempt a 57-yard field goal, which it made.

Other coverages

Schwartz has other coverages to throw at offenses at third-and-long, and most are soft zones. He might throw in some man defense in the red zone or blitz against a certain quarterback. But the objective is typically the same: Don’t get beaten over the top. Limit the damage. Get off the field.

In this 2016 game, for instance, the Packers were ahead, 24-13, in the fourth quarter and had the ball just past midfield. The Eagles couldn’t allow any more points, so Schwartz called a more aggressive defense — a Cover 2-man — to try to keep Green Bay out of field-goal range.

It worked.

But there were five plays last season in which the Eagles allowed a first down on a third or fourth down of 15 yards or longer, and each was with a defense other than the picket fence.

The most devastating came in the Titans’ loss last September. The Eagles were up, 23-20, after kicking a field goal on the first possession of overtime. Tennessee, on the ensuing series, faced fourth-and-15 on its own 31. Schwartz called a combo regular Cover 2 and inverted Cover 2.

The Eagles had the middle of the field covered, but safety Corey Graham (lower underneath defender) lacked awareness of the receiver behind him and didn’t get wide enough. Quarterback Marcus Mariota got the ball out in time and hit Taywan Taylor for a 19-yard gain.

Should Schwartz have called his sticks defense there? Based on its previous success, maybe. But if Graham had simply done his job, the Eagles would have likely walked out of Nashville with a win.

The defensive coordinator had this to say last November after the Eagles allowed their latest long conversion.

Schwartz: “All calls look good if they work. All calls look bad if they don’t work.”

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Addendum: Some fans here and on social media have continued to voice their criticism of the picket fence defense because the yards allowed can, in certain situations, flip the field in the other team’s favor after a punt. While yards are yards, the numbers -- at least in terms of the Eagles -- don’t back up this claim.

In the 37 times that Schwartz has used his sticks coverage, the Eagles have allowed an average of 6.8 yards per play. In all the other instances when they faced a third or fourth down of 14 yards or longer, they allowed 9.3 yards. While circumstance, as explained above, could play some role in the latter’s higher number, it’s still a significant difference.

And even if those coverages are considered too soft by Schwartz’s critics, they are the norm. Defensive coordinators are rarely aggressive in similar situations. Blitzing could pressure quarterbacks and force turnovers, but the risks are often considered too great vs. a conservative approach which will often accomplish the same goal: getting the ball back for your offense.