Tom Hateley's penalty for Motherwell against Celtic has sparked debate, after the midfielder placed the ball on the edge of the spot.
Referee Steven McLean allowed the kick to be taken, despite the protests of goalkeeper Fraser Forster, but was he correct to do so?
It is generally accepted that the ball is placed on the middle of the mark, which is drawn 12 yards from the goal line. Is it legal to move it somewhere else on the spot?
We've asked our anonymous referee, a top official, to clear up whether McLean was correct to allow the kick to be taken.
At a penalty, does the ball need to be placed in the middle of the penalty mark? Or, like at a corner kick, does just part of the ball need to be touching the mark?
The exact position of the ball is not specified in the Laws of the Game. Law 14 deals with the penalty kick and states solely that "the ball must be placed on the penalty mark."
McLean was correct to allow the kick to be taken from this position. As long as part of the ball is touching the mark, it is legal for it to be taken.
FIFA's Laws of the Game only stipulate the penalty mark must be 12 yards from goal. Could a team have a smaller or even an alternative penalty mark, say an X, as long as it is 12 yards away?
Law one, dealing with the field of play, addresses this. Within each penalty area , a penalty mark is made 11 meters, or 12 yards, from the midpoint between the goalposts and equidistant to them.
A mark could easily be a cross but is more likely to be a +, if it is not a traditional spot.
Do FIFA have clear laws on this, or are referees given guidance on how to deal with such a matter in training?
The state of the penalty mark is not a major concern as, on many occasions, the mark can become worn and divot-like.
Players tend to move the ball around slightly but still technically put the ball on the mark.
So the referee was correct to allow the kick to be taken?
Yes. The Laws of the Game only state the ball must be placed "properly" on the penalty spot. As long as it is touching anywhere on the mark, the kick can be taken.