Obstruction or nothing

[DG]

I don't rule obstruction unless the runner was actually obstructed.

In the original post I have obstruction because the runner was knocked to the ground and a play was made on him. I don't imagine the catcher would be throwing the ball down there except to make a play.

If the BR was rounding 1b and bumps into F3 but was not making an attempt to 2b, as he would not be on a clean single being returning to infield, I don't see obstruction there.