Interference/obstruction vs. fair/foul

[KentuckyBlue]

Partner and I disagreed on a question inspired by a routine play in an NSA slow-pitch game (probably ASA would apply here too). Fortunately, this is how far we have to go for controversy this season. I bring it here for Mike & Co. to resolve.

Inning's first batter lifts a 40-foot pop-up halfway up the 1B line. Ball is bending and will clearly fall foul by a couple of feet. F1 and F3 charge for the catch across BR's base path within the three-foot lane as BR runs for first.

There wasn't any collision, the catch was made. BUT....had there been a crash, could there have been an interference or obstruction call considering that the ball was already going to be foul?

I said yes, and I would have called interference/out since runners must yield to fielders making a play. Partner said that if he had called anything it would have been obstruction with the BR awarded first, but partner probably wouldn't have called obstruction because the ball was (going to be) a foul. So what do the Panel-O-Experts think?

Evil wrinkles on the above: Would I be correct in calling against any player if I thought they had veered to cause a collision? Also...what if F1 and BR had collided and then F3 made the catch?