For those in Yorkshire Rio Ferdinand committed the cardinal sin in 2002 – he crossed the divide.
He joined a list of players who’ve gone from Leeds United to Manchester United.
A decade earlier a certain Eric Cantona had swapped Elland Road for Old Trafford, and we all know how that went.
But Ferdinand, then an England international with the world at his feet, wanted to move.
Player power is a part of the game nowadays and there is a school of thought that suggests they perhaps have too much power.
Transfer deals are played out in public and Ferdinand would’ve had no problem doing so 19 years ago.
Then Leeds chairman Peter Risdale had taken the club to the semi-finals of the Champions League.
They spent big, something he has since said was a mistake, but were unable to retain their lofty position.
Leeds’ most expensive signing was the £18m then spent on a 22-year-old Ferdinand.
It was a British transfer record and made him the world’s most expensive defender.
Less than two years later though and he was gone, but it was who we went to that caused a stir.
Ferdinand knew of United’s interest and went and sat in Risdale’s office for six hours until a deal was thrashed out.
The move wasn’t played out in public, but the six-time Premier League winner would’ve taken it that far had he needed to.
“I fortunately enough was never put in a position where I had to go in all guns blazing, but trust me, if I’d needed to i would have,” he said previously on BT Sport.
“At Leeds I went and sat in Mr.Risdale’s office and just sat there and waited for about five, six hours and said I’m not going until you sort out the deal for me to go to Man Utd.
“I didn’t go public, I didn’t need to go. We got to a compromise, we got to a situation where he felt he was getting the right part of the deal and I got my opportunity to go to Man Utd.
“But I was adamant I wanted to go because that was the right time and the right move for me.
“If he had said no and put a firm wall up I reckon I probably would’ve gone public with that because I feel, as a player, its a short window in terms of being able to be successful.
“10 – 15 years if that. You’ve got to make decisions that are a little bit selfish.
“As a fan and as a football club I get that you might not understand that, but it works both ways.”
Leeds had slapped a £30m price tag on Ferdinand leading up to his departure.
Fan anger only increased when the young defender went back on claims he made in a Sun interview where he said he didn’t want to leave the Yorkshire club.
Risdale says in his book ‘United We Fall’ that he was delighted to see his star defender publicly declare his affection for Leeds.
Perhaps though it wasn’t as genuine as he’d hoped with Ferdinand supposedly responding by saying: “You know that was for the supporters… me and you both know I’m off!”
United’s offer started at £22m. Risdale held out and held out before eventually getting his desired £30m.
Ferdinand would return to Elland Road two months later wearing red.
Jeers greeted him as he ran onto the pitch and it was an afternoon to forget as Harry Kewell headed in a winner for Leeds.
Ferdinand would have the last laugh though, his former side were relegated two years after he left.
His departure signalled a mass exodus, perhaps a sliding doors moment that further angered Leeds fans.
The now 42-year-old would go on to win several league titles, two League Cups and a Champions League.
There’s no doubt that Ferdinand contributed to the undeniable chasm that exists between Leeds and their bitter rivals.