What does Boxing Day have to do with boxing?
late 13c., from Old French forclos, past participle of forclore "exclude" (12c.), from fors "out" (Modern French hors; from Latin foris "outside;" see foreign) + clore "to shut" (see close (v.)). Senses in English influenced by words in for-. Specific mortgage law sense is first attested 1728. Related: Foreclosed; foreclosing.