The most shocking game result in Week 17 of the 2019 NFL season was unquestionably Miami’s 27-24 win over the Patriots. New England was playing for the AFC’s two-seed, which they ceded to the Chiefs with the loss, so it wasn’t like Bill Belichick was resting guys out there. And while it was no surprise that the Patriots’ offense was unspectacular — Tom Brady completed 16 of 29 passes for 221 yards, two touchdowns, and one interception, and Sony Michel led the team with 74 yards and a touchdown on 18 carries against the Dolphins’ sub-par defense — it was the performance of New England’s defense that raised some red flags as the defending Super Bowl champs head into the postseason.

Throughout most of the season, it’s been the defense that has kept the Patriots humming while the offense has performed in fits and starts at best. Through the first 15 weeks in 2019, New England allowed the NFL’s fewest completions (261) for the second-fewest passing yards behind San Francisco (2,666), for the fewest touchdowns (10), the lowest completion percentage (56.01%), the lowest yards per attempt (5.72) and the most interceptions (25). The Patriots allowed an opposing QBR of 57.39; the Bills ranked second in that time period at 76.73, You could argue that New England faced a relatively weak slate of opposing quarterbacks overall, but still, on that side of the ball, things were going at a historic level.

And then, over the last two weeks, it seems to have fallen apart. Against the Bills in Week 16 — a game the Pats still won to take their 11th straight AFC East title — and in that Dolphins loss, New England has allowed a completion rate of 60%, 42 completions for 548 yards, three touchdowns, no interceptions, and an opposing QBR of 98.99 — only five teams have been worse over the last two weeks of the season in that regard.

The most worrisome character in this particular regression is cornerback Stephon Gilmore, who looked like the runaway Defensive Player of the Year through the first 15 weeks of the season. Then, he allowed just 38 receptions on 82 targets for 444 yards, no touchdowns, six interceptions, and an opponent passer rating of 32.8. Among cornerbacks taking at least 50% of their teams’ defensive snaps, only J.C. Jackson, Gilmore’s teammate, allowed a lower passer rating.

But over the last two weeks — that tight win over the Bills and the upset loss to the Dolphins — Gilmore has allowed nine catches on 16 targets for 180 yards, one touchdown, no interceptions, and an opponent passer rating of 131.5. Among cornerbacks taking at least 50% of their teams’ defensive snaps in that time, only eight have allowed a higher passer rating.

And it’s not just Gilmore. Jackson has been more vulnerable. Safeties Devin McCourty and Duron Harmon have not been as efficient and opportunistic of late. Perhaps most disconcerting for those aficionados of Belichick’s defensive brilliance over time is the seeming breakdowns between cornerbacks and safeties.

The first real example of things going wrong came with 7:25 left in the third quarter of the Bills game, when quarterback Josh Allen hit receiver John Brown for a 53-yard touchdown on a deep over route. The Patriots are running a man blitz here with McCourty as the deep safety, and Gilmore covering Brown in the defensive left slot. Defensive lineman Lawrence Guy forced a pressured throw from Allen, but Gilmore lost Brown on the fake outside to the seam, didn’t pick him back up, and McCourty was out in the weeds. It’s tough to remember an instance this season in which New England’s secondary was this out of sync.

“We kind of thought we had a beat on the play and we tried to be aggressive on it,” McCourty said after the game. “A call I made in the secondary where we try to be a little more aggressive and after you get beat on a touchdown, I came to the sideline and I’m like, ‘We’re not going to run that anymore.’ I think, like always, guys in our secondary, we move on fast and I think we always come to the sideline and understand exactly what it was and why a bad play happened for us, and then we fix it and got right down to it. A call that we liked coming into the week to be aggressive, and they kind of dialed up the perfect call against what we were doing, threw it away and then kept playing.”

Well, if that was a lone rogue incident, we wouldn’t be talking about a downward trend that really blew up against the Dolphins — the same Dolphins team that just fired Chad O’Shea, their offensive coordinator. So, there’s that. Well, in this game, Gilmore was exposed as he’d rarely been in a Patriots uniform, especially by Miami receiver DeVante Parker, who caught eight passes for 137 yards, and most of them against Gilmore.

Parker’s first reception, a 28-yarder from Ryan Fitzpatrick with 7:50 left in the first quarter, was another example of Gilmore in a schematic pinch.