We still might not know how good New England’s defense is, and we don’t quite know what it is, either. However, we do know that the Patriots surrendered the fewest points in the NFL this year — and they did it with a defense that shirks any one specific definition.

Bill Belichick and defensive coordinator Matt Patricia’s defense is built upon versatility. And that comes from a group of five shape-shifters: lineman Trey Flowers, linebacker Dont’a Hightower, cornerback Logan Ryan, and safeties Patrick Chung and Devin McCourty. With each player capable of moving around the field to effectively play multiple roles against either the run or the pass, it doesn’t matter what personnel grouping the Patriots have on the field. Whether it’s a run or a pass, New England has the players to defend either option.

For the Falcons, there are always options. The key to Atlanta’s success this year has been its ability to identify the opposition’s weakness, and then attack it with both the run and the pass from the same formations. Matt Ryan has a potent mix of multifaceted players at his disposal — tight ends that can block and catch, a running back duo that can run and catch. As such, the Falcons balanced a seventh-ranked rushing attack with a league-best passing offense.

Opposing defensive coordinators just never know when the Falcons are going to throw or when they’re going to pass. So, do you bring out your base defense against multi-running-back or multi-tight-end looks and risk losing effectiveness in coverage? Or do you bring in an extra defensive back and lose that size and strength against the run?

But maybe New England’s figured out what to do when faced with an impossible question: refuse to answer it.

The Patriots’ versatility starts with the variety of their scheme. Nominally, New England has run a 4–3 scheme for the past several years, but it’s common to see Belichick and Co. tailor the defensive design to the skill sets of the available talent. On Sunday, we’ll see elements of both the 4–3 and the 3–4, and on some plays, we’ll even see 4–3 and 3–4 principles combined into a unique one-gap/two-gap hybrid. In a league where traditional position designations grow ever more irrelevant, New England’s defense has been the archetype of adaptability.

Like just about every other defense in the league right now, the Patriots’ base defense has five or more defensive backs on the field, whether it’s a “big-nickel” package (which features three safeties), a nickel look (with three cornerbacks), dime personnel (with six defensive backs), or some other permutation. But the Patriots don’t run those subpackages like everyone else. By moving Flowers, Hightower, Ryan, Chung, and McCourty around based on opposing personnel groups and formations, the Patriots can match up with whatever the offense presents.

“They have very good players all around,” Falcons offensive coordinator Kyle Shanahan said this week, “players that are interchangeable, that can be pass rushers, that can be linebackers, that can be corners, that can be safeties.”

Throughout the season, Chung’s been the prime example of this versatility. On one play, he’ll drop down into the box from his safety spot and play coverage against the slot receiver, on the next he’ll match up with a tight end, and on the one after that, it’ll be a running back. This flexibility gives the Patriots the ability to cover against basically any personnel grouping, and when teams run the ball, he’ll play the role of a de facto linebacker, filling gaps and tackling ballcarriers. And it’s not just the fact he’s capable of playing all these roles, it’s that he can execute them all at a very high level. As Belichick said two weeks ago, “Without [Chung] … you’d have to [run our defense] differently, let’s put it that way … There’s a lot of guys who can go out there and take up space, but they really can’t perform against that level of competition the way you need it.”

Meanwhile, Chung’s safety partner is a former Pro Bowl cornerback who made the permanent switch to safety four seasons ago. In his seventh year, McCourty has the capability to play deep as the center fielder in New England’s scheme, but can also walk up toward the line in the Patriots’ big-nickel looks and can capably cover a receiver, a tight end, or a running back out of the backfield. He sees the field and tackles like a safety, but covers like a corner. Without McCourty’s effectiveness in both of those aspects, Belichick said in late December, the Patriots “wouldn’t be able to do [all the different things we do on defense] as well.”

Elsewhere in the secondary, cornerback Logan Ryan, who started the season playing on the outside, transitioned inside to play in the slot more in the second half of the year. From that spot, he’s proved to be an excellent coverage nickelback, but it’s his tackling that makes it possible for the Patriots to run those nickel looks against good running teams. Because he’s taking the place of a linebacker or defensive lineman on the field, teams will frequently run right at that potential vulnerability. If he was a liability taking on blocks or as a tackler, New England wouldn’t be able to keep him on the field. Instead, Ryan led all corners with 92 tackles this season.

The interchangeability extends into the linebacking corps and up to the defensive line, too. Middle linebacker Dont’a Hightower can play the run and the pass with equal aplomb. In fact, he’ll even line up like a defensive end and rush the passer in some looks. By moving him around, Belichick and Patricia constantly find ways to keep the offense guessing; the harder it is to know where pressure’s coming from, the harder it is to set your offensive line protections. They do the same with defensive lineman Trey Flowers, who lines up on the edge on base downs before sliding inside to rush in clear passing situations. If the offense still runs, the 265-pound Flowers is stout enough to play the block-absorbing role of a 3–4 defensive end normally reserved for players 40 to 50 pounds heavier.

The Patriots’ versatility on defense starts with these five guys, but it doesn’t end there. Malcolm Butler is a shutdown corner who can stick to the opposing team’s no. 1 receiver in coverage, which means he’ll find himself playing just about everywhere in a formation. Malcom Brown and Alan Branch plug up the middle, which allows New England’s linebackers to flow to the football, but they’re both capable of shooting gaps and affecting quarterbacks dropping back to pass, too. With a diverse group of linebackers and defensive ends in Rob Ninkovich, Chris Long, Shea McClellin, and Kyle Van Noy, the Patriots can field coverage-heavy looks or pass-rush-focused groups, depending on down and distance. Eric Rowe and Duron Harmon give New England multiple options in nickel/dime packages, and a few other role players can come in and play down-and-distance or matchup-specific roles.

Put it all together, and New England can field an uncommon amount of looks to counter the firepower Atlanta can throw out there this Sunday, both in the run game and against the pass. Few defenses this year have shown the flexibility to adapt to a Falcons scheme that targets so many of its weapons and uses so much of the field. Because if any defense is built to stop an unpredictable, position-vague offense like the Falcons, it’s this one. They’re a positionless defense for a positionless NFL.