What does Boxing Day have to do with boxing?
Old English scamful "modest;" see shame (n.) + -ful. Meaning "disgraceful, causing shame" is from c.1300. Related: Shamefully; shamefulness. Middle English shamely (adv.) "shamefully" for some reason has fallen from use. Old English scamlic (adj.) "shameful, disgraceful," but this also could mean "modest."