While it has always been considered a breach of etiquette to stand on or close to the line of play (unless attending the flagstick) there is now a prohibition on caddies standing in this area after a player begins to take their stance. This also applies to Partners (and Partner’s caddies) in fourball, foursome, and team competitions and would incur the General Penalty (Two strokes or Loss of Hole). Please be aware of this when playing matches and warn your opponents if you see them about to contravene it. The penalty can be avoided by backing away and re-taking the stance.
Golf Rules Guru 