F3 was not in posession of the ball and hindred the batter/runners progress. Textbook obstruction, defensive players not in posession of the ball may not hinder offensive runners.
Comp thanks for the explanation on one, I've learned something new, always a good thing.
On this one I'm not trying to be obtuse but doesn't the fielder have a right to field the ball? Does this not extend to trying to catch a throw from another fielder? I mean I've seen a lot of throws over the years sail up the 1B line towards HP side and the 1B's natural reaction is often to try and catch it and swipe tag the runner - at least if they are a good 1B that's what they'll do. I can't ever recall seeing this called obstrution unless the throw was so horrible the 1B had less than zero change to get a glove near it.
edit: oops should have read SoCal... first, I think he clears this up that 1B came off the bag into path of runner so I'm now assuming throw was awful and 1B did obstruct.