Boxer in the kids singing scene?

At the beginning, a man who is plainly supposed to be a boxer and was probably a retired one in reality, congratulates Deborah Kerr and then mock punches the priest. I do not think he is credited but I suspect he was pretty well known at the time. There were numerous boxers who went on to acting, usually in small roles such as this. (Jake La Motta played a bartender in The Hustler, for example.) My guess is that the guy is Maxie "Slappy Maxie" Rosenbloom -- does anyone know?