What does Boxing Day have to do with boxing?
"to cause to work too hard," 1520s, from over- + work (v.). Old English oferwyrcan meant "to work all over," i.e. "to decorate the whole surface of." Related: Overworked; overworking.
"work beyond a person's strength," 1819; see overwork (v.). Old English oferweorc meant "a superstructure, sarcophagus, tomb."