Obstruction or an out?

[SC Ump]

It sounds to me that F3 was not making a play on a batted ball and was .... receive a thrown ball, so we can't call the B/R out for interfernce.

If the collision happened before F4 made the out, I believe that I would have to call obstruction... even if I thought F4 would have beat the B/R to the bag.

If the collision happened after F4 made the out, I believe the out would stand.