Flag down/Slow whistle

[stevesmith]

Flag down, slow whistle, Team A is throwing the ball around the box trying to set up a play. A1 is pressured by B1 and steps outside the box trying to run around B1 and make a pass to A2 back inside the box.

The game I was watching last night was stopped as soon as A1 stepped outside the box. I questioned it to the people sitting near me (long-time knowledgable fans). They all agreed with the call. I looked it up in the rulebook and can't find anything that says to stop the game when the ball leaves the box with possession on a flag down. There are 10-12 other reasons listed for stopping the play, but leaving the box isn't one of them.

I was told the "spirit/intent" is to make sure Team A is still in attack mode. That may be, but it's not in the rulebook! Can anyone help me with this???