{"numbering":"asc","slides":[{"index":1,"title":"","image":"https://www.nbcsports.com/sites/rsnunited/files/archive/assets_media_gallery/boston/2019/03/29/bill_belichick_greg_schiano.jpg","caption":"

Bill Belichick is going back to the drawing board -- and he may need to use it this year.

Greg Schiano's sudden departure Thursday leaves the New England Patriots without a defensive coordinator entering the 2019 season. And with last year's play-caller, Brian Flores, taking his talents to South Beach, Belichick either must hire a new D-coordinator or assume the duties himself.

There is precedent for the latter, as Belichick has operated without a defensive coordinator before. But if you look back over Belichick's two decades in New England, there's a familiar pattern to those cases: If he finds a coordinator he likes, he'll stick with that person for a while. If not? He'll just do the job himself.

Let's run through Belichick's defensive coordinators over the last 20 years -- just four in total, and one in the last nine years -- to explain what we mean.

Photo via AP Images

"},{"index":3,"title":"2000: No coordinator listed","image":"https://www.nbcsports.com/sites/rsnunited/files/archive/assets_media_gallery/boston/2019/03/29/bill_belichick_1.jpg","caption":"

Belichick operated without a defensive coordinator during his first season in New England. It didn't go so well, as the Patriots allowed 334.6 yards per game while finishing 5-11.

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"},{"index":5,"title":"2001 to 2004: Romeo Crennel","image":"https://www.nbcsports.com/sites/rsnunited/files/archive/assets_media_gallery/boston/2019/03/29/bill_belichick_romeo_crennel.jpg","caption":"

Belichick wised up and brought on Crennel -- who coached with him on the New York Giants' staff under Bill Parcells -- the following year. That decision paid off in spades, as the Patriots won three Super Bowls in four seasons under Crennel thanks to a stifling defense that allowed the NFL's sixth-fewest points per game in 2001, second-fewest in 2003 and third-fewest in 2004.

Crennel's success earned him national notoriety, as he left Belichick's staff in 2005 to become the head coach of the Cleveland Browns.

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"},{"index":7,"title":"2005: Eric Mangini","image":"https://www.nbcsports.com/sites/rsnunited/files/archive/assets_media_gallery/boston/2019/03/29/eric_mangini.jpg","caption":"

Mangini seemed like a natural successor to Crennel: He spent the previous four seasons as New England's defensive backs coach and attended the same university (Wesleyan) as Belichick.

But the Mangini Experiment was short-lived. The Patriots were a middling defense in 2005 (16th in points allowed) and gave up 27 points in a Divisional Round loss to the Denver Broncos. Mangini then bolted from the Patriots to become head coach of the rival New York Jets, where he later set off the "Spygate" scandal in 2007 by accusing New England of illegally filming his team's signals.

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"},{"index":9,"title":"2006 to 2009: Dean Pees","image":"https://www.nbcsports.com/sites/rsnunited/files/archive/assets_media_gallery/boston/2019/03/29/bill_belichick_dean_pees.jpg","caption":"

Perhaps feeling spurned by Mangini, Belichick hired a familiar face in Pees, who spent two years in the 1980s as an assistant coach at Navy under Belichick's father, Steve.

The Pees-Belichick marriage didn't result in a championship, but it still worked very well: The Patriots boasted a top-five defense by points allowed in three of Pees' four seasons, including New England's historic 16-0 regular-season campaign in 2007.

Pees opted not to renew his contract after the 2009 season, however, leaving Belichick without a defensive coordinator yet again. So...

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"},{"index":11,"title":"2010 and 2011: No coordinator listed","image":"https://www.nbcsports.com/sites/rsnunited/files/archive/assets_media_gallery/boston/2019/03/29/bill_belichick1.jpg","caption":"

... Belichick decided to go it alone. Again.

Belichick operated without a defensive coordinator for the next two seasons, with mixed results: His 2010 squad allowed the eighth-fewest points in the NFL (19.6 per game) but choked in the playoffs, giving up 28 points in a Divisional Round loss to the Jets. His 2011 defense wasn't as stout (21.4 points per game, 18th in the NFL) but got hot in the postseason to help secure a Super Bowl berth.

After two coordinator-less years, though, it was time for Belichick to settle down with another trusted candidate.

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"},{"index":13,"title":"2012 to 2017: Matt Patricia","image":"https://www.nbcsports.com/sites/rsnunited/files/archive/assets_media_gallery/boston/2019/03/29/matt_patricia_bill_belichick.jpg","caption":"

Belichick found his man in Patricia, who had worked on his staff since 2004 and got the defensive coordinator title in 2012.

After a disappointing finish in his first season -- 28 points allowed in both of New England's playoff games -- Patricia went on to coach some very solid Patriots defenses that helped Belichick reach three Super Bowls (and win two) during his six-year tenure.

Before Patricia left to become the Detroit Lions' head coach in 2018, he was the longest-tenured defensive coordinator in the NFL.

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"},{"index":15,"title":"2018: No coordinator listed (Brian Flores called plays)","image":"https://www.nbcsports.com/sites/rsnunited/files/archive/assets_media_gallery/boston/2019/03/29/usatsi_12104895_133468180_lowr.jpg","caption":"

With Patricia out the door, Belichick took a hybrid approach last season, not naming a new defensive coordinator but letting linebackers coach Brian Flores call plays.

This arrangement seemed to work, as the Patriots finished with the seventh-best defense in the NFL and delivered one of the best defensive performances in Super Bowl history to defeat the Los Angeles Rams.

Belichick doesn't have another Flores waiting in the wings, though -- his son, safeties coach Steve Belichick, is the only defensive coach currently listed on the Patriots' staff -- so with Schiano no longer lined up and no close connection waiting in the wings, history suggests Belichick may assume primary play-calling duties for the first time in nine years.

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"}]}

Who will be Patriots' defensive coordinator? Belichick's past offers clues