Very often, especially for the R and U, although ALL officials can benefit from a well placed, targeted comment, our voice sends a more efficiently received message, even more than our whistle. An Umpire's consistent reminders "to get up easy", "it's over" or other such passive remarks helps establish his presence around the action.
Most people instinctively behave better, when they PRESUME they're being observed by an authority figure close by, whether they're actually being watched, or not. Umpires, Linesman (O & D) and Linebackers often have a "special" conversation going on privately. (D-backs are a separate breed).
Referee's comments, "Pass/kick is away, stay off him" can set a tone that once players are aware of, they respond to whether they hear it, or not. Treating Captains with verbal respect can pay significant dividends, should you subsequently need their support or assistance with their teammates.
99% of what may be said to players, INSIDE the lines, is intended, specifically for players on the field. If they want to share those comments with people OUTSIDE the lines, that's up to them, but there's no requirement that we share or explain anything (unless, of course, we choose to) to anyone.
Choice of language is important, presuming a player's mother can hear you is a safe guideline.
