[kbowton]

I definitely would not call obstruction. Straddling the base is acceptable and it is clear there was going to be a play at that base so it is obvious that the runner would slide. By straddling the base you keep the main side of the bag available to the runner. The runner should slide for safety reasons on a play.

As for the rule book, I have been told by the State Umpire-In-Chief that it is merely a guideline. You are the one making the judgment call and as long as you give a definite "call" it doesn't matter if someone disagrees. You are the one running the game. No one sees the play the way you do.