In the context of a protest which R&D will have to decide, we have a Law 14 question to resolve. The ref called a PK. The kicker was identified, etc. He blew the whistle for the kick to be taken. Before the ball was struck, a teammate of the kicker ran into the box. The kicker struck the ball. Seeing the teammate streaming in, the ref blew the whistle. The keeper hearing the whistle made no play on the ball and it went into the net, having only been kicked by the kicker. The ref awarded an IFK to the defending team.
Law 14 doesn’t exactly cover a dead ball that goes into the net from a PK. Had the ref not blown the whistle, it would be either a retake if it went in the net , etc. One school of thought that has emerged is under advice to referees it tells us the ref determines when the PK is complete, and having done so by his whistle, the restart is governed by the team that committed the violation, thus the IFK was correct. The other is the kick was not complete at the time of the whistle, so retake. While not stated, some refs have earlier whistles in youth games if for no other reason to reduce likelihood of injury. With the infringing player coming on strong, a decision to shut it down sometimes occurs.
USSF answer (October 19, 2010):
The whistle was blown but the ball was not yet in play when the teammate of the kicker entered the penalty area. No goal was scored because of the infringement by the teammate of the kicker. Warn the teammate (if it was his first infringement of Law 14, or caution if it was a second offense) and retake the penalty kick.