What does Boxing Day have to do with boxing?
Old English bereafian "to deprive of, take away, seize, rob," from be + reafian "rob, plunder," from Proto-Germanic *raubojanan, from PIE *reup- "to snatch" (see rapid). A common Germanic formation (cf. Old Frisian birava "despoil," Old Saxon biroban, Dutch berooven, Old High German biroubon, German berauben, Gothic biraubon). Since mid-17c., mostly in reference to life, hope, loved ones, and other immaterial possessions. Past tense forms bereaved and bereft have co-existed since 14c., now slightly differentiated in meaning, the former applied to loss of loved ones, the latter to circumstances.