I think this custom really caught on in the late '60s. It's hard to find footage of players congratulating each other this way before then. It continues today. It's lovely in a way.
But where and how did it originate? How did such a -- let's face it -- intimate gesture catch on in a sport defined by its machismo?
The butt pat
Re: The butt pat
When you are in a warrior environment showing some form of affection with your comrades has always been around. In ancient Sparta the warriors were at times sexually involved with one another and it wouldn't have been uncommon during time of war in more modern times for troops to feel just as close (if not closer) to one another then they were to their own blood families. Football is at least a big enough threat to the players well being to earn a little tap on the rear end by the comrades who are fighting along side one another. And to be honest I am sure it has been around ever since the sport started.