T/F - A fielder in possession of the ball can never be guilty of obstruction.

[Steve M]

I'm not aware of any instance when a fielder who has the ball can obstruct. Though, I do seem to remember some clinic discussion about either F1 or F3 making a feet first sliding grab of a bunt near the 1B line and tripping the B-R after gloving the ball. I'd have to think that could be either an obstruction or unsportsmanlike call - depending on what it looked like.