Law- 14 penalty kicks.
The Defending Goalkeeper
As stated by the rules of Fifa
The defending goalkeeper:
• must remain on his goal line, facing the kicker, between the goalposts until the ball has been kicked.
My question is does the keeper have to keep a part of their body on the line until the ball is kicked? Or does the keeper have to keep both feet on the line until the ball is kicked? It is allowed for keepers to move side to side so the feet obviously do not have to be on the goal line. I would guess this question relates to the plane being broken. When watching any professional games it seems that the keeper is allowed to move forward as long as a part of the body is on the goal line in the plane between the goalposts. I am looking for some clarification on this rule because as I have gray areas of rules.
Answer (October 15, 2014):
As you note, the Law tells us that the defending goalkeeper must remain on his goal line, facing the kicker, between the goalposts until the ball has been kicked. A later portion on Law 14, in the back of the Law book under Interpretation of the Laws of the Game and Guidelines for Referees, reiterates that the referee must confirm, before the penalty kick is taken, that the goalkeeper is on the goal line between the goalposts and facing the kicker. If the goalkeeper violates these instructions, the kick may be taken; however, if the ball enters the goal, the goal is awarded. If the ball does not enter the goal, the kick is retaken.
To answer your question specifically, the goalkeeper must remain on the line. No specific body part is mentioned, because it is traditional that the goalkeeper be upright, both feet on the line. He or she may move along the line, but must not move forward or backward.
Not sure where any grayness might enter the picture, unless you take into account poor work by lazy referees at all levels of the game, those who allow the ‘keeper to move forward (or sometimes backward), which is not permitted until AFTER the ball has been kicked.
And one correction: The Laws of the Game are not written by FIFA. They are written by the International Football Association Board, of which FIFA is a member. FIFA publishes the Laws for all.