OBS

[EMD]

It the "interruption of the flow of the play" that is really at issue, I think

It seems to me you have an two plays to content with.
BR rounded first base and tripped over F3's foot. He is protected to return because as you described he was making a turn toward second so that he may advance if F9 does not field the ball correctly. After the trip, he gets up to return, and would have been safe with or with out the obstrcution call -no harm no foul. End of play #1. When the ball is throw away he attempts to advances to second, (play #2) IMO, he advanced at his own risk.

Isn't this the same logic used for base awards? For example, B1 is awarded first on ball 4, then attempts to advance beyond the base and is tagged out. He did this at his own risk.

What is the difference?