[greymule]

You can't always make a precise determination at the time of the obstruction (a fact their answer concedes). But, as IrishMafia says, you have to adjust to what happens after the fact. And runners do recover differently.

Why should you decide immediately how you're going to call the play? What if it's players you haven't seen and after you decide the runner gets 3B, you see that he has blazing speed and that the outfielder retrieving the ball has no arm?

The book says that in all cases the obstructed runner gets the base he would have reached without the obstruction. If after the play it's obvious he would have scored, why lock yourself into a decision that had to be made before you had all the information?

What if the batter hits a line drive into right center, and as the outfielders chase it, the runner crashes into F3, stumbles, and falls. You decide he gets 3B, but then the ball gets past everybody and it's clear that it's an easy home run, except that the BR hobbles lame into 2B and stops, holding his knee? Now what?

I disagree strongly with their advice.