walk-on (n.)youdaoicibaDictYouDict[walk-on 词源字典]
"minor non-speaking role," 1902, theatrical slang, from the verbal phrase walk on, attested in theater jargon by 1897 with a sense "appear in crowd scenes," from walk (v.) + on (adv.). Meaning "actor who has such a part" is attested from 1946. The sports team sense is recorded from 1974.[walk-on etymology, walk-on origin, 英语词源]