Alex Ferguson introduced a rule about shirt-swapping after Ruud van Nistelrooy returned to the Manchester United dressing room with a Manchester City jersey in his hands.
Ferguson didn't take kindly to the sight of his striker holding the shirt of United's rivals and unleashed his infamous hairdryer treatment on the Dutchman.
Van Nistelrooy was told in no uncertain terms that United's jerseys were not his to give away as he pleased and the legendary United manager then put a rule in place which banned his players from trading tops after domestic matches.
Former Red Devils captain Gary Neville revealed the story on the
Quickly Kevin, Will He Score? podcast, going into detail on Ferguson's furious reaction.
"I always remember, after that game Ruud van Nistelrooy had swapped shirts with a City player," Neville said. "The City player had come up to him and swapped shirts.
"He said, 'You do not give away one of those shirts. They're my shirts. They're this club's shirts, they're not your shirts. You're just wearing them temporarily. That's not your possession to give away.'
"He stopped us swapping shirts in domestic games.
"I think he said after that game, 'I should let the fans in here. I should let the fans come in here and speak to you.'"
Van Nistelrooy left United in 2006 after scoring 150 goals in 219 games for the club following a falling-out with Ferguson.
