FOXBOROUGH, Mass. -- When Bill Belichick was hired as New England Patriots coach in 2000, he made it clear through his initial first-round draft choices what type of defense he intended to run.

Patrick Chung has proved to be effective in coverage against top tight ends and tough-minded against the run. Mark J. Rebilas-USA TODAY Sports

It was a base 3-4, and Belichick invested top picks in defensive linemen Richard Seymour (2001, No. 6 overall), Ty Warren (2003, No. 13 overall) and Vince Wilfork (2004, No. 21 overall), in part because those players uniquely fit the two-gapping scheme and projected to be on the field for the majority of snaps.

Nineteen years later, with Super Bowl LII as the most recent example, the Patriots’ base 3-4 defense has diminished in usage and importance. The significant majority of snaps (80-90 percent) are now played in sub packages, and for the Patriots, it’s most often their “Big Nickel” grouping, with three safeties, two cornerbacks, two off-the-line linebackers and four defensive linemen.

In Super Bowl LII, the Patriots had their top three safeties -- Devin McCourty, Patrick Chung and Duron Harmon -- on the field for 63 of 75 defensive snaps. While the results weren’t what they hoped for in that game, the three-safety approach was consistent with how they played for significant stretches of 2017.

It's a point that is topical to highlight, as it accompanies an ESPN.com piece on potential trade suitors for Seattle Seahawks safety Earl Thomas.

Do I really think the Patriots -- with their entire safety corps returning in 2018 -- would deal for Thomas?

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It’s highly unlikely.

But a case could at least be made that no team in the NFL values the safety position as much as the Patriots based on their usage of the Big Nickel, so it’s at least worthy of a conversation.

Along those lines ...

Why Big Nickel? As the game has become more spread out offensively, with more three-receiver packages and/or tight ends who are essentially big receivers, it has put more stress on defenses to match up. So the Big Nickel provides a nice middle ground -- a defense that adds an extra defensive back to support in the passing game, but one that, in theory, remains stout enough against the run with a safety who can play some linebacker-type duties.

What makes it work? Versatility within the safety group. McCourty entered the NFL in 2010 as a cornerback and can sometimes be tapped to fill those responsibilities. He also has moved down to more of a linebacker position, where his sure tackling and toughness have shown up. Chung also has experience playing the “star” position (inside corner), and has proved to be effective in coverage against top tight ends and tough-minded against the run. Harmon is more of a pure center-field type, but also has some versatility to do different things. That creates options that can be used on a game-plan basis, or even on a play-by-play basis. This season, McCourty, Chung and Harmon are back, as well as top backups Jordan Richards and Nate Ebner and practice squad players Damarius Travis and David Jones. From an NFL-wide perspective, the Texans are an example of a team that might be envisioning more Big Nickel possibilities after signing versatile free agent Tyrann Mathieu and drafting Justin Reid in the third round to pair with returning starter Andre Hal.

Importance of depth. With the Patriots running the majority of their snaps in the Big Nickel, it almost makes the No. 3 safety a starter, and thus, the No. 4 player on the depth chart is more than the traditional backup who might be viewed as less likely to play on defense. One injury and that No. 4 player becomes a critical piece, or it forces the defense to go away from the package to something altogether different.

History lesson. It was a few years ago when Belichick traced the origins of the nickel defense to Washington coach George Allen in the early 1970s, explaining how Allen would bring in a defensive back for a weakside linebacker. “It was just a one-for-one substitution of a better pass defender in passing situations for a linebacker,” Belichick explained, noting that, as a Colts assistant in 1975, he broke down a 1974 Redskins-Rams game, with the Redskins reacting to the Rams using a not-often-seen-before package of two tight ends, two receivers and one back. “It created a lot of problems for Washington’s defense because it was always a strongside, weakside 3-on-2, 4-on-3 matchup. That personnel group ended up creating a real problem because you were able to get three receivers out to either side after the ball was snapped; defense didn’t know what it was. That really struck me.” Things have obviously evolved since then, but in simple terms, the Big Nickel has essentially become a Patriots modern-day version of what Allen was trying to combat: It’s the versatile defense that -- if played well with good personnel -- can match up to any offensive grouping.