PU Positioning

[Rufus]

Coach here with a question. Was watching an MLB game, can't recall which, and there was a play at the plate. BR hit a single to LF and the throw came home, but was up the line toward 3B. As the C moves to field the throw and attempt to make a play I notice the PU moving from behind the plate up the first base line in foul territory.

I'm not interested in slamming or questioning his positioning, but wanted to know when do you ideally make the decision on where you need to be to see the play? I know from reading some previous posts that you don't want to be moving when viewing a play if possible but, in cases like this where the throw may be not where you expect it to be, it seems like you almost have to be.

Guess I'm wondering a bit about the mechanics of when you decide to move to get in position and what dictates where you stand. Thanks in advance.