Can a player verbally declare his ball to be lost?
A player may not render a ball lost solely by declaration. A ball can only be considered lost when (a) it is not found or identified as his by the player within five minutes after the player’s side or his or their caddies have begun to search for it; or (b) the player has made a stroke at a substituted ball; or (c) the player has made a stroke at a provisional ball from the place where the original is likely to be or from a point nearer the hole than that place.
