Team A is granted a direct free kick within shooting distance of the goal. Team A’s shooter asks for 10, the referee notifies the players that the restart is on his whistle and marks off the 10. The referee then gives the signal to start play. As Team A’s shooter begins running up to the ball but before she kicks it, a player in Team B’s wall moves toward the ball thinking, incorrectly of course, that the whistle made it good to go. Neither the kicker nor the kick is affected by the encroachment and the ball goes over the crossbar for what under normal circumstances would be a goal kick.
Should there be a rekick because there was encroachment or is it ignored when it has no effect on the play? If there must be a rekick, is that still true if the player had scored with the free kick?
USSF answer (November 3, 2008):
Our guidance to referees on this sort of situation is contained in the USSF publication “Advice to Referees on the Laws of the Game”:
13.3 ENFORCING THE REQUIRED DISTANCE
If the referee decides to delay the restart and to enforce the required minimum distance, the referee must quickly and emphatically indicate to the attackers that they may not restart play until given a clear signal to do so. Under these circumstances, an attacker who restarts play without a signal should be verbally warned and, upon repetition, be cautioned for unsporting behavior. The free kick in such cases must be retaken, regardless of the result of the original kick. An opponent who moves closer to the spot of the kick (from any direction) before it is taken must be cautioned and shown the yellow card if the referee has delayed the restart to ensure that the opponents are at the minimum distance.
If one or more opponents fail to respect the required distance before the ball is properly put into play, the referee should stop the restart to deal with this infringement as required by the Law. The free kick must be retaken even if the momentum of play causes the ball to be kicked before the referee signals. The infringement plus the referee’s decision to deal with it cancel any apparent restart regardless of a delay in announcing the decision. However, referees are also expected to consider whether the infringement on the minimum distance was trifling (had no effect on the freedom of the attackers to restart) and, if so, to refrain from issuing a caution and to allow play to proceed.
The referee is expected to deal with opponents who fail to respect the required distance, even in situations in which they were induced to do so by attackers appearing to put the ball into play, but where the ball was not kicked (touched with the foot and moved).
An attacking team may exercise its right to take a free kick when the players see an advantage to do so even with an opponent closer than the minimum distance. However, they may not thereafter claim infringement of the distance requirement if the ball is kicked to an infringing opponent who is able to control the ball without moving toward it. In this case, because the attacking side has considered the encroachment trivial, the referee must accept what he or she has seen.
On the other hand, when the attacking team has exercised the option to restart play quickly and the opponent closer than the required distance moves toward the ball and performs an act that makes a difference in the play, such as blocking the kick, that player has committed an offense that must be dealt with firmly in accordance with the Law. After the referee has cautioned the failure to respect the required distance, the original free kick must be retaken as required by Law 13.
That citation contains all the information you need.