Umpire interference with batter-runner

Question
What happens when an umpire impedes a base runner?

Situation: Bases loaded, 2 outs, bottom of last inning. Batter hits a deep line drive into the right center gap for a certain grand slam HR (no fence) under normal circumstances, but the field ump crosses into batter-runner's path after she rounds 2nd and collides with her preventing her from scoring the game tying run. After the collision the ump starts talking to the batter-runner without calling dead ball, so she (out of respect to the umps) stands there and listens and only gets to 3B when she easily could have scored to tie the game.

I never got a chance to talk to the ump after the game to understand his positioning, or why he talked to the batter-runner after the collision.

What should be the call?

Answer
Hi Ed,

That is 1 slow umpire, you're telling me that the b-r rounded 2nd before the field umpire could come inside the diamond?

He then collides w/ the b-r and starts a conversation during a live ball?

By rule obstruction is the act of a fielder, we have no rules on "umpire obstruction". In this case and I'm sure I've never had one like it, using the reasoning that in most cases an umpire is part of the field ie when a thrown ball hits an umpire it continues to be live, when a batted ball hits an umpire after it has passed an infielder (exc the pitcher) it remains live so as a tournie uic I would have to rule the play stands as it was.

I never got a chance to talk to the ump after the game to understand his positioning, or why he talked to the batter-runner after the collision.
I wish you had, I would like to hear what he said.

Mark