Aaaay, the Fonz
Henry Winkler has a small role in this movie. Happy Days debuted on Jan. 15, 1974. Crazy Joe debuted one month later on Feb. 15. Since a movie needs a longer lead time to bring to theaters than an episode of a TV series requires, it's likely that Henry finished his scenes in Crazy Joe, which was filmed in New York City, before heading to Los Angeles to start his role in Happy Days.
One of the few lines Henry has is, "Ever since Richie died all our action has been going to Vince." That made me think of Richie Cunningham -- Ron Howard's character on Happy Days.