obstruction?

Only if it was intentional, and that would be a very tough sell.  As described, I have an out.

I agree that it has to be intentional, but the fact he's taking off his mask with a play at the plate imminent is one of those things that makes me go "Hmmm..."

One of my pet peeves in the last few years has been catchers/coaches taking advantage of the no contact rule and catchers working up the line forcing the runner to change direction to avoid a tag and inevitably being out because he is not sure what to do or has to slow to change direction.  I have never seen an umpire in this situation favor the base runner and call obstruction.

They should be. What fielders are allowed to do without the ball changes slightly from set to set, but this is most likely obstruction in all of them. Whatever set you use, learn it, ask questions here, and learn what questions to ask of umpires.

Also, speaking of pet peeves, there is no "no contact rule." All national sets allow contact; its the manner in which it is initiated that determines legality/illegality.