NFL assumptions are risky, at best, but assuming Mike Zimmer is indeed safe and will not be fired before Thursday's season-ending news conference, he will have clawed his way to the podium as a survivor who's tied for ninth in current NFL head coaching longevity.

Top 10. And he was hired in 2014. Talk about pressure.

The Vikings coach will rank fifth in the NFC. First in the NFC North. And stand among only five survivors out of the 14 head coaches with defensive backgrounds hired since 2014.

Of those five — the others are Atlanta's Dan Quinn, Buffalo's Sean McDermott, Detroit's Matt Patricia and Tennessee's Mike Vrabel — none made the playoffs in the Great Offensive Explosion of 2018.

The Jets' Todd Bowles, Denver's Vance Joseph and Arizona's Steve Wilks fell from that defensive-minded list Monday when they became three of the eight casualties of the 2018 season.

Wilks went a league-worst 3-13 in his head coaching debut. Then he became the 10th coach since 2000 to be fired after only one season.

Yes, it's a "production business," as Vikings safety Harrison Smith put it when asked Sunday about the harsh reality of a team with Super Bowl expectations going 8-7-1 and missing the playoffs. But the pain and discontent being felt this week comes in colors other than the usual Purple.

When the 2019 season opens, 19 of the league's 32 head coaches will have been hired since the end of the 2016 season. Five were hired in 2017, six in 2018 and eight more to come in 2019.

Of the 11 coaches still standing from the 2017-18 classes, eight are coaches with offensive backgrounds. So, yes, there's an ongoing shift to that side of the ball as Chicago's 40-year-old Matt Nagy heads toward NFL Coach of the Year honors a year after Sean McVay won the award at 31.

Speaking of McVay, he'll be a grizzled graybeard of 33 when the 2019 season opens. He'll also be tied for 14th in current head coaching longevity.

Bill Belichick, of course, is the king. Five Super Bowl wins and Benjamin Button as your quarterback tends to keep a guy around a couple of decades.

In January of 2000, Belichick was introduced as Bill Parcells' replacement as Jets coach. A day later, Belichick bolted for the Patriots.

It cost the Patriots a first-round draft pick to untangle the mess Belichick created. But it might have been the best trade in NFL history.

There were nine members of the new head coaching class of 2000. Seven of them, including Belichick, were coaches with defensive backgrounds.

Including that class, there have been 129 NFL head coaches hired this millennium. Ninety-five (73.6 percent) have since been fired. Seven retired.

Three left for the college ranks, including Bobby Petrino, who quit on the Falcons after 13 games in 2007.

Of those 129 hires, 66 had offensive backgrounds, 62 had defensive backgrounds and one — Baltimore's John Harbaugh — came from a special teams background. Since 2013, the hires have been decidedly lopsided with 27 being coaches with offensive backgrounds and 15 with defensive backgrounds.

Of the 27 with offensive backgrounds, 13 have since been fired (48.1) percent. Of the 15 with defensive backgrounds, 10 have been fired (66.7).

New England, of course, has had to make only one of those 129 hires this millennium. The Raiders have made a league-high nine, starting with Jon Gruden and, well, ending with Jon Gruden.

The Browns and Dolphins are searching for their eighth coaches since 2000. The 49ers, Bills and Lions are on their seventh coaches.

The Bay Area owns four of the 10 head coaching one-and-dones since 2000. The 49ers fired Jim Tomsula and Chip Kelly in back-to-back years (2015-16).

The Raiders fired Art Shell after going 2-14 in 2006 and Hue Jackson after going 8-8 in 2011.

So, yeah, it's not easy meeting expectations in today's NFL. Especially as a defensive-minded coach. Something Zimmer is aware of as he survives a fifth season and looks toward a sixth one.

Mark Craig is an NFL and Vikings Insider. Twitter: @markcraigNFL. E-mail: