PROTOCOL FOR INJURED PLAYER AT PK

Question:
Another question for you posed to me by a referee. I’ve massaged the wording a bit to keep those involved nameless but didn’t make any changes impacting the situation or ensuing decision. Here goes:

At an NCSL U16D2 boys game there was a young referee in the center with two adults as his assistants. One of the assistants was the centers father.

Early on in the 2d half with the score having recently been tied at 1-1, a foul was called resulting in a Penalty Kick restart. Dad thinks it was the correct decision from his view from the half. The defending player committing the foul was hurt. Instead of the coach coming on to the field to aid the injured player, two of his team mates helped him off the field. Before the player was off the field (and the sub on the field), the referee allowed the PK to be taken, which resulted with a goal being scored. Assistant Referee, Dad, raised his flag and called the referee over, advising the referee he should not have allowed the PK to be taken since the substitution hadn’t been completed, and the correct way to restart was to make sure the defending team had 11 players on the field, and to have the PK retaken. After giving this advice consideration, the referee ordered the penalty kick to be retaken which this time was saved. The attacking team was not happy. The defending team went on to win 4-1, the attacking team did not protest. The referee reportedly handled the rest of the game without incident.

Granted, the referee should have done better by ensuring the injured player was properly substituted before signaling for the PK to be taken and this wouldn’t have been an issue. But since the signal to start was given the question is can the referee now change his mind and stop play? Or since the signal was given, play restarted and a goal was scored, should it be allowed to stand? Or, in the interest in Fair Play, did he do the right thing by ordering the PK to be retaken after the injured player was substituted?

My initial thought is haste makes waste and since there didn’t appear to be any infraction related to encroachment or improper player positioning during the taking of the penalty kick, the goal should have been allowed since this wasn’t really a substitution based on the way the situation was described to me. How did I do regarding my take of the situation? You’re never too old to learn.

USSF answer (June 19, 2011):
The failure to allow a substitution is not the problem here. The referee’s error was in allowing the penalty kick to be taken while the injured player and his teammates were otherwise engaged, Although these players could not “defend” against the penalty kick, they had the right to be present on the field in positions permitted by the procedures for a penalty kick. The referee, who allowed the teammates to help the injured player off the field, should have waited for the two teammates to return to those positions.