NFL or soccer -- which sport has the hotter coaching hotseats?

Graziano: Rivera firing won't be the last change in Carolina (1:35)

Dan Graziano reports that Panthers owner David Tepper's decision to fire head coach Ron Rivera is just the beginning of the coaching and organizational changes ahead for Carolina. (1:35)

It wasn't quite the exit that "Riverboat" Ron Rivera should have had. A more appropriate finale for the Carolina Panthers head coach would have been a win-or-bust 2-point conversion going wrong in a Week 17 play-in game

Instead, the Panthers were upset by a rookie quarterback, a mediocre team and the billionaire Carolina president David Tepper. He pulled the trigger on his head coach mid-season, after a home loss to the Washington Redskins, apparently to get a competitive advantage in the market ahead of other teams who may be weighing up a change.

Moving a coach on mid-season is the exception to the rule in the NFL, in sharp contrast to the Premier League and most major European soccer leagues. Even this week, Napoli topped a Champions League group that contained last season's winners Liverpool, beating Genk 4-0 in their last group match on Tuesday and by Wednesday morning manager Carlo Ancelotti had been sacked.

Eight Premier League clubs have changed managers in 2019, and bottom-of-the-table Watford have even managed to fire two managers this season, more than the number of games they've won (one in 16 so far).

By contrast, Rivera and former Washington Redskins head coach Jay Gruden earlier in the season, are the only two head coaches to have been relieved of their duties in the NFL so far this season.

So why are the timelines so different?

The absence of promotion and relegation in the NFL and the severe financial implications that either of those can have for soccer clubs is perhaps the most significant reason for this.

Most NFL teams are in mathematical contention at least for a playoff berth for much of the season. For those that aren't, the worst-case scenario is a half-full stadium and tedious dead rubbers for a few weeks before hitting the reset button in time for the following year. Being an NFL owner is like being the kid in the arcade who has unlimited credits for any game he wants to play. Doesn't mean he'll play it well, but he'll always get to play.

Access to suitable replacements is also a key factor here. In the NFL, many prospective candidates are locked into existing co-ordinator roles, especially for teams who are doing well and eyeing the playoffs. This can range from veteran former head coaches or hot shot young play callers. It even extends to head coaching jobs in college, where the successful teams play deep into December and beyond. The volume of elite options in between jobs are limited.

Even if a co-ordinator wanted to move mid-season, the complexity of the NFL makes it a virtual impossibility for someone to walk into a new team, compute both the offensive and defensive game plans, get their heads around a 53-man roster as well as the practice squad and familiarise themselves with their entire coaching staff in a short space of time. Building a successful NFL team needs plenty of time and headspace and a mid-season move to a team without your blueprint applied is a high risk for all concerned.

As well as mid-season firings being far scarcer in the NFL than in professional soccer, so too are short-term appointments, relatively speaking. "One and done" seasons -- head coaches lasting in the job for only a year -- are rare, with NFL owners accepting that a turnaround takes longer for all concerned. Soccer team owners rarely apply such a patient approach.

Since 2000, only 10 teams in the NFL have jettisoned their main guy after just one season. This comes from the understanding that the inherited roster is either indifferent or poor in most cases because the teams have been struggling or under-performing for too long. The relationship between head coach and the front office is also instrumental in a more long-term approach as the personnel units rebuild a roster more aligned to the vision of the new coach, as opposed to his predecessor. In contrast, almost two thirds of the 92 managers of professional English soccer sides have been in the job for 18 months or less.

It's typically the NFL teams that favour continuity and consistency the most that succeed. The four longest-serving head coaches in the league right now have all won Super Bowls during their time -- Bill Belichick was hired by the New England Patriots in 2000, Sean Payton by the New Orleans Saints in 2006, Mike Tomlin by the Pittsburgh Steelers in 2007 and John Harbaugh by the Baltimore Ravens in 2008.

All four of the above teams are currently in the playoff picture this season, with three (Ravens, Patriots and Saints) among the favourites and set for a high seeding. Tomlin is also on a shortlist for Coach of the Year for keeping his Steelers competitive despite so many injuries.

In contrast, the Cleveland Browns have had 11 head coaches since 2000 and haven't been to the Super Bowl once. Not even close.

It's unlikely any further changes will be made in the NFL over the next few weeks, whilst Manuel Pellegrini is odds-on to be shown the door at West Ham any day now. But when Black Monday comes around -- the day after the final regular game of the season -- heads start to roll, as teams cull their dead wood and begin the rebuild.

Browns head coach Freddie Kitchens is on thin ice having started the season as a decent Super Bowl shot in many people's eyes. A few players weren't shy about talking up their chances at the start of the season but the team has under-performed on the field and off the field. The apparent lack of player control is either because Kitchens can't handle them, or because of the culture he's engendered. Either way, it's not a good look.

For the same reasons, unless the Cowboys pull off a miracle and win the Super Bowl, head coach Jason Garrett is set to be moved on. Failing to find success with a talented bunch, they have underwhelmed to such a degree that Dallas owner Jerry Jones has finally run out of patience.

There's buzz that Garrett may stay in the NFC East though if the New York Giants move on from their head coach Pat Shurmur. Big Blue have failed in successive appointments now to fill the shoes of two-time Super Bowl winner Tom Coughlin, and Cowboys fans, who have turned on their current head coach, would revel at the idea of Garrett ending up steering a big rival.

Coughlin isn't having the same kind of success running the operations at the Jacksonville Jaguars, and it seems that head coach Doug Marrone is another coming to the end of the road. He'll join the collection of coaches who came so close to a place in the Super Bowl.

Cincinnati Bengals head coach Zac Taylor should be given another year in Cincinnati, despite the woeful one-win record. A tough season has somehow not diminished his reputation as a dynamic and progressive coach.

Detroit Lions head coach Matt Patricia may get a stay of execution as he nears the end of his second season. He can cite the loss of quarterback Matthew Stafford as a contributing factor but the next few weeks, and how the Lions battle, could be critical.

Jets head coach Adam Gase was given a public vote of confidence by his bosses -- something that often signifies the end is near when it happens in English football -- and there is a suggestion that despite seemingly weathering the storm, Gase may get moved on. Again, a strong finish to the season should tip the balance in his favour.

At the Atlanta Falcons, head coach Dan Quinn is a long way from that fateful Super Bowl LI night in Houston, where the Falcons were on the wrong side of the greatest comeback in Super Bowl history. The window has been gradually closing, and Quinn will almost certainly find himself out in the cold.

With half a dozen or so NFL gigs up for grabs, owners will look at a combination of veterans as well as considering playing the hot hand and using co-ordinators who are in the middle of successful seasons.

Recognisable faces currently in the college system could make an appearance also.

"There's a very real chance that Jim Harbaugh is back in the NFL next season. His dream job at Michigan has not worked out but he'd land a head coaching gig in the pros because of his track record" says Ben Isaacs, resident college expert on the Nat Coombs podcast.

Other names to look out for, according to Isaacs, include Chris Petersen who is "an outstanding coach who has stepped down at the University of Washington and has been coveted by NFL teams for years." Isaacs also picked out David Shaw "who has had a down year at Stanford, but NFL execs still love him" and Matt Rhule who "has unexpectedly taken Baylor to the brink of the College Football playoffs and is one to keep on your radar."

Editor's Note: The Nat Coombs Show podcast joins the ESPN network for four episodes a week. Join Nat and his guests every Monday, Wednesday, Friday and Saturday as they get you up to speed with the latest goings on from the NFL with a unique, transatlantic twist.