Every so often, the NFL produces a moment that can rock fans to their very core.
It could be a historic game - like one we saw last season when the underdog Philadelphia Eagles won the Super Bowl against the New England Patriots.
Or, it could be a moment that football fans will never forget for all the wrong reasons.
Because every so often, a player, coach or owner will commit one of the biggest crimes possible in professional sports - betrayal.
So, here are five of the best... or worst, moments of betrayal in NFL history.
1) BOBBY PETRINO QUITS THE FALCONS MID-SEASON
Petrino made the step up from coaching college football in 2007 when he joined Atlanta in a five-year deal worth $24 million.
However, things quickly went south for the franchise, as Mike Vick was sidelined for most of the season before it had even kicked off.
With the Falcons bottom of their division with a 3-10 record in December, Petrino walked out - and took a job as the head coach at Arkansas.
It's the manner in which he left that was heavily criticised - apparently only informing his players by leaving a four-sentence laminated note at each locker. Brutal.
2) BRETT FAVRE JOINS THE MINNESOTA VIKINGS
Favre will go down in history as one of the NFL's greatest quarterbacks - and he accomplished everything with the Green Bay Packers between 1992 and 2007.
In fact, he was such a legend, that the team retired his number four jersey.
However, fans won't forget the decision he made in 2009 when he joined the Minnesota Vikings after a year in New York.
Seeing a Packers legend retire anywhere else would have been bad enough for fans, but it's the fact he went to Minnesota, the team's biggest rival - and retired there.
To make things worse, he had one of his best ever seasons in 2009 and led the Vikings to the NFC Championship game.
3) BILL BELICHICK LEAVES THE NEW YORK JETS - FOR THE NEW ENGLAND PATRIOTS
Back in 1999, when assistant head coach Belichick left the Jets, his decision wasn't seen as a massive deal.
He wrote his resignation note on a napkin, during a press conference when he was supposed to be announced as the teams new head coach - and even that wasn't the worst part.
It was when news broke of where he was going, that his move became a problem - because he joined the Patriots, New York's biggest AFC East rivals.
19 years, five Super Bowl rings and one Tom Brady later, Jets fans still haven't forgotten where Belichick began, before jumping ship to Foxborough.
No doubt, a mere mention of Belichick will set their fans on edge, perhaps thinking about what could have been for them.
4) DARRELLE REVIS SWITCHES BETWEEN THE JETS AND THE PATRIOTS
Much like Belichick, cornerback Revis isn't a stranger to betraying Jets fans. He first left New York in 2013 - after he was traded to Tampa Bay.
But following a poor season, he was released by the Buccaneers and created his own massive moment of treachery.
Revis signed a deal with the Patriots, turning his back on the Jets in the process. But that turned out to be a pretty good move for him - as he won a world championship in 2015.
Even a return to New York the following year may not have been enough to build bridges with his old fanbase. After all, he only spent two more seasons there before moving to Kansas.
5) ART MODELL MOVES THE CLEVELAND BROWNS TO BALTIMORE
In 1996, Modell shook the sports world by announcing his intention to move the Browns to Baltimore.
His decision turned the entire city of Cleveland upside down. Perhaps the worst part is that he entered secret discussions to move his team to Maryland.
This came after he promised they would never leave Cleveland - and publically opposed the Baltimore Colts move to Indianapolis a few years before.
Understandably, the reaction he received was hostile. In the end, Modell had to settle for changing the Browns to an expansion franchise - and the Baltimore Ravens were born.
In Cleveland, they kept their beloved Browns - and a deal was struck to re-activate the Ohio franchise in 1999.
Which of these betrayals do YOU think is the worst in NFL history? Have YOUR say in the comments below.News Now - Sport News