I argued that one of them HAD to verbalize it and they both were adament that they did not have to. Bases were loaded with one out. and all the runners knew it was pop up, but when nothing was called , they took off as the ball dropped between the pitcher and first baseman untouched. The pitcher threw home to get the runner from 3rd. Both umpires conferred after the play, said they did not have to verbalize the call and the runner was out advancing on his own. Are you required to verbalize? I have always verbalized it.