This is from a rehearsal of West Side Story. They're rehearsing one of the jazzier sections of the score. The strings don't get it. So Bernstein draws their attention to the first trumpet player, who is Wilmer Wise. At that time Wise was well-established in the studio scene in New York City (this was a pick-up orchestra for a recording). Earlier in his career he'd been the first black musician to play with the Baltimore symphony. Think of this post as a comment on a previous one, the conversation between Bernstein and Ellington.