Yeah, at first I thought it was a pretty silly double steal, but when Jim Kaat explained what the thinking may have been, it made sense. Halladay was pitching strikes, it was 1-2 on Fielder, so chances are he was going to swing and hopefully make contact. The runners moving would mess up the infielders, giving Prince a better chance to sneak a grounder through. It just so happened that it was a ball Prince couldn't swing at in the perfect spot for the catcher to come up throwing.