Assume you are the AR.
The center referee calls a direct kick. He stops play to mark off the ten yards. All the defenders line up evenly across the field. An offensive player lines up next to the wall even or slightly in front of the wal l(less than 10yds).
Just before the kick is taken the players in the wall step forward to do an offside trap. The ball is chipped over the wall to the offensive player that was even with the wall and he scores.
Since the wall moved forward within the 10yds, it is actually encroachment. The offensive player that was where the wall was originally placed now looks like he was in an offside position.
How should the AR rule? Offside, or allow the play to continue and the goal count.
USSF answer (September 28, 2008):
Provided all is precisely as you say — and the kicking team’s player remained where he was when the wall was set and that all the opponents moved forward, making them all nearer to the ball than the required ten yards — there is no offside infringement to worry about. Why? Because the defending team committed the first infringement by violating Law 12’s requirement that a player must respect the required distance when play is restarted with a corner kick, free kick or throw-in. Thus the referee may simply invoke the advantage and allow the goal. In fact, if the referee felt so inclined, he or she could easily caution all members of the wall for committing that infringement.
In this case, the AR should leave the flag down. The team that lives by the offside trap also die by the offside trap.