Football legend Johan Cruyff was critical of Manchester United's 'biggest mistake' after Sir Alex Ferguson's retirement in 2013.

Any player who did move out of position was replaced by someone else ... of one of the greatest players of all time, Johan Cruyff, who was seen as the most important component of the system.

Put simply, it means all 10 outfield players in a team are comfortable in any position. So if a defender wants to go ... The brains behind it all was the Dutch captain and Ajax star player - Johan ...