off-base (adv.)youdaoicibaDictYouDict[off-base 词源字典]
"unawares," 1936, American English, from off (adv.) + base (n.); a figurative extension from baseball sense of "not in the right position" (1898), from notion of a baserunner being picked off while taking a lead.[off-base etymology, off-base origin, 英语词源]