I think I made up a rule and award

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ASA 16U Rec. Runner on 3rd ball four on batter. As BR is walking to first the first base coach is looking at her a point towards second (left hand going back and forth in front of his belly). At the same time the D Coach walks fast out of the dugout calling time. I give him a hand gesture to wait, but he keeps coming walking right in front of the BR. I kill the ball call coaches obstruction and award the BR 2nd and the girl at 3rd home.

Can't find anything in the book to support my call, but here was my thinking. The coach walking out on the field during live ball play basically stopped everything including the opportunity of the BR to continue to second, and the possibility that the pitcher would make a play on her, thus allowing the runner on 3rd to attempt home.

Is there anything in the book that supports my call or did I make up a rule and award?