Why do we call today Boxing Day?
What is known is that the holiday is the feast day of Saint Stephen (Good King Wenceslas). There has also been an association since the early Christian period with charity - metal boxes were left outside churches.
In Britain Boxing Day has always been seen as the holiday of the lower classes - with gifts to the servants and sporting events for the masses. Today it is equivalent of the US Black Friday after Thanksgiving - the make or break day for retailers.