Yahoo Sports: Ah, the post-match (and sometimes halftime) tradition of players exchanging sweat-soaked shirts with members of the opposing team. According to FIFA, the first recorded instance of this ritual was in 1931 when the French team requested their English opponents' shirts to "commemorate their historic 5-2 victory at Colombes." Yet, the most famous swap -- and the one that sparked the modern craze -- was when legends of the game Pele and Bobby Moore did it after the 1970 World Cup match between Brazil and England.
Well that wasn't a mystery for me at all.
knew about this