After the food excesses of the previous day, when everyone was feeling a little bloated, a little athletic exercise was called for. Great Rings were set up in the woods, and anyone who dared was allowed to enter the ring and compete in a little boxing match with all comers.
This also helped to alleviate the social pressures between the Lords, who had many fat turkeys and lots of food on the previous day, and the poor peasants who worked the land and were barely at subsistence levels.
So the contests of Boxing Day were the only day of the year that a peasant could strike a Lord with impunity and not lose thier head or their lands. It also was a time when the people could judge their lord's courage and fortitude; if a Lord would not enter the ring, people knew him for a sissy and they would gossip mockingly about him throughout the new year, undermining his political authority and causing the King to look askance at him.
Thus it was important for a Lord to make a good showing at the matches; even if he was defeated, the people gave him props for showing up, and for abdicating his social and political privileges and joining them in the Ring. Many a Lord, although perhaps not being as efficient or as smart as the people or King would desire, was nonetheless beloved and adored for a good right cross or particularly-agile footwork, and for good sportsmanship in taking the terrific blows of the ironmonger's son (who was quite the terror in the ring). Even more beloved were the Lords who chose to keep their Boxing Day scars and missing teeth, displaying them proudly throughout the year as a mark of solidarity with their tenant-farmers.
Thus today we celebrate this time-honored and most democratic of holiday customs in rememberance of our illustrious forebears.
Put 'em up!!!!
[ editor's note: this is a gag I loved to do in RL for many years; I even had the boxing gloves! ]