A run that scores shall be unearned if the runner reaches first base after his time at bat is prolonged by a muffed foul fly, because of interference or obstruction or because of any fielding error. No run shall be earned when scored by a runner whose time on base is prolonged by an error, if such runner would have been put out by errorless play, or if the runner's advance is aided by an error, a passed ball, or defensive interference or obstruction, if the scorer judges that the run would not have scored without the aid of such misplay.