This has come up a number of times, but I’ll be danged if I can find any threads on it. Anyway, you know the routine, something happens, and one person starts clapping. Then another. Then more. Then everyone.
IIRC, the *earliest this attested was in “Brubaker” (1980). In the 1974 Roy Campanella biopic “It’s Good to Be Alive,” there is a similar scene. Toward the end of the movie, after Winfield’s Campanella makes his first publica appearance in the baseball stadium. He chokes up after saying a few words. Then, one player starts clapping, then the others, etc.
*Again, I can’t be sure since I can’t find any of the old threads.