When do you finally step in?

[greymule]

It wasn't that it was my job to watch the fair/foul ball. I simply saw it land a yard fair, and both F5 and R3 had blocked PU's view of the line.

Yes, you eat the blown foul call—in most cases. But if PU calls foul on a ball that actually hit the foul pole above the fence, that can be changed (I know that dead ball cases are different). And what about winning run on 3B in bottom of 7th and, let's say, 1 out? BR hits a line drive that lands obviously inside the LF line and then PU calls it foul. R3 scores. Do you still send him back and eat that one, too?