A stroke added to your score for a rules infraction such as hitting a ball out of bounds, into a penalty area you cannot play from, or declaring a ball unplayable. In scoring terms it is the most expensive shot in golf, because you pay the stroke and you usually surrender position as well. Penalty strokes are the single largest avoidable cost in an amateur round, and their frequency rises sharply as handicap rises. Because strokes gained charges a shot with everything it costs you afterwards, a tee shot that ends in a penalty is penalised twice over, which is why driving accuracy dominates scoring below scratch and barely registers on tour.