What does Boxing Day have to do with boxing?
"to acquire by irregular means," 1915, alteration of dialectal scrunge "to search stealthily, rummage, pilfer" (1909), of uncertain origin, perhaps from dialectal scringe "to pry about;" or perhaps related to scrouge, scrooge "push, jostle" (1755, also Cockney slang for "a crowd"), probably suggestive of screw, squeeze. Popularized by the military in World War I. Related: Scrounged; scrounging.
[1909+; probably fr British dialect scrunge, ''squeeze,'' hence ''steal,'' semantically parallel with pinch]