What does Boxing Day have to do with boxing?
Old English walu "ridge," as of earth or stone, later "ridge made on flesh by a lash" (related to weal (n.2)); from Proto-Germanic *walo (cf. Low German wale "weal," Old Frisian walu "rod," Old Norse völr "round piece of wood," Gothic walus "a staff, stick," Dutch wortel, German wurzel "root"). The common notion perhaps is "raised line." Used in reference to the ridges of textile fabric from 1580s. Wales "horizontal planks which extend along a ship's sides" is attested from late 13c.
A mark raised on the skin, as by a whip; a weal or welt. v. waled, wal·ing, wales
To raise marks on the skin, as by whipping.