The Eagles have turned the quarterback sneak into the least sneaky play in the playbook. There was no mystery about what Philadelphia were planning when Jalen Hurts lined up with nine teammates between the hashes on the San Francisco one-yard line in the NFC Championship game, half of the group in four-point stances.

Nor did the call change after the 49ers stopped Hurts for no gain. One play later, from an identical formation, Philly’s quarterback took the snap and plunged forward to his left, forcing his way into the end zone with some help from tight end Dallas Goedert and running back Boston Scott behind him, shoving him over the line.

It is a strategy they have used all season, to punishing effect. Eagles center Jason Kelce channels Anchorman with his line that “92% of the time, it works every time,” but the real numbers aren’t far off. During the regular season, the Eagles converted 29 of their 33 quarterback sneaks into first downs or touchdowns.

No team has ever used the play so prolifically. When the NFL’s Football Operations team dug into the data three years ago, they found that Tom Brady led the league with 157 sneaks since 2001 – 85 more than second-placed Drew Brees. To frame that statistic in a different way: even the league’s “Master of the QB sneak” averaged fewer than 10 a season.

“I like the way they’re doing it,” said Brady when he was asked about the Eagles’ approach in December. “They’re kind of making it like a rugby scrum a little bit, putting a lot of bodies in there, which is kind of a new take on it.”

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More than a scrum, the closer parallel in rugby union may be a maul, when a ball-carrier is held by an opponent but has not yet gone to ground. Teammates bind together around them, overlapping arms and grabbing each other’s shirts to create an overwhelming mass of bodies that keeps the play moving upfield.

Why had NFL teams not imitated the tactic sooner? Pushing a ball-carrier to help them advance has been legal since 2005. Although the league still has a rule against “assisting the runner”, it only prohibits pulling a teammate forward with the ball, as well as the use of “interlocking interference, by grasping a teammate or by using his hands or arms to encircle the body of a teammate in an effort to block an opponent.”

Not every coach can be familiar with every detail of the NFL’s 245-page rulebook. There were so many queries raised over the Eagles’ QB sneaks early this season that the league’s officiating department had to send out a video to every team clarifying which forms of assisting the runner were permitted.

Stuart Lancaster, the former head coach of England’s men’s national rugby union team, offers another possible reason why nobody had tried the move before. “It takes courage to do something different,” he tells the Guardian. “I think there’s a lot of teams out there who could be innovators and bring more ideas across from rugby if they opened themselves up to that.”

He has some experience in this area. Lancaster was invited by the Falcons to conduct a series of coaching sessions with players in 2016 after meeting the then Atlanta head coach Dan Quinn at a leadership conference.

The focus back then was on open-field tackling techniques, but Quinn, now defensive coordinator for the Dallas Cowboys, got in touch again this season asking if Lancaster had any advice on how to counter the Eagles’ heavy goalline package.

“[Philly’s sneak play] is not dissimilar to a driving maul or pick and go near the line,” says Lancaster, now a coach for Irish club side Leinster. “I showed him some footage of rugby teams defending those situations successfully near the line.

“The first thing is that you’ve got to match their numbers. If you’ve got five and they’ve got eight, you’re going to lose. You might get away with seven versus eight if you’re good enough, but not five. Then you’ve got to win the shoulder battles. You’ve got to get lower, you’ve got to push them upwards and backwards. On the snap, you’ve got to accelerate forward, because you need momentum if you’re going to win the inches.”

The Cowboys did not heed his advice, Lancaster says, continuing to leave too few players in the box when they faced the Eagles in week 16, though the Saints got it right without his help a week later. “Having been to the Falcons, I think most people there had very little awareness of rugby,” he adds. “I expect that’s true for a lot of NFL teams.”

While the Eagles’ sneak play may look something borrowed from another sport, their head coach Nick Sirianni has not made that link publicly himself. Philadelphia have been effective with QB sneaks since before Sirianni got the job, converting 11 out of 11 on their run to win the Super Bowl in the 2017 season, when Doug Pederson was in charge.

Some of it comes down to making the most of your personnel. Kelce is one of the league’s best run-blocking centers, and the rest of the Eagles’ interior offensive line are similarly formidable. Then there is Hurts, a 223lb “gym rat”, in Sirianni’s description, who can squat almost three times his body weight. Leaning into their combined strengths makes perfect sense.

Similarly, one other reason that no rival had leaned into this rolling maul strategy may simply be that they do not want to risk the health of their most important player. The surest part of any sneak is that your quarterback will get hit. Patrick Mahomes, the man behind center for Philadelphia’s Super Bowl opponent, Kansas City, dislocated his kneecap on such a play in 2019 and has not been allowed to run one since.

For Lancaster, that is not a good enough reason for most teams to deny themselves a powerful strategy. “It’s a pretty safe play,” he insists. “The quarterback is surrounded by 10 100kg man mountains. Injuries in rugby happen more in the dynamic contact areas, when you get into the open spaces.”

There is still an art to the Eagles’ QB sneak, even when it is predictable. Sirianni said in November that the coaching meeting to discuss the team’s tight-formation red zone plans was the longest, and most enjoyable, of every week. Philadelphia has used varied pre-snap motions and line shifts to bring different players into position to give Hurts that all-important shove across the line.

No doubt there will have been more hours poured into the scheming this week, a fresh wrinkle designed to attack a perceived weakness in Kansas City’s defence. The Chiefs will probably know when the sneak is coming, but may struggle to stop it all the same.