Here's what I had:
Catcher pops up, bat hits him hard in the thigh and he (not on purpose) goes to his left, down almost to his knee in pain.
I look down to see how bad he took it. I look up and pitcher is trying to throw home.
Catcher jumps up and a few feet back to the plate to try to catch pitcher's throw, but cannot cover the ground in that state.
Ball goes to the backstop, I think back through the play.
I call "Time! That was interference! Batter is out!" and send the runners back to their bases, declaring "All runners return to the base they held at the time of the pitch"
As I explained to the offensive coach, the act of the batter recklessly throwing the bat and hitting the catcher, took the catcher out of the ability to make the play.
I think I could have declared R3 out since it would have been an easy 1-2-3 double play.
Offensive coach accepted that it was INT, then started fishing with "well usually INT is called immediately."
I countered telling him that I needed to make sure they were coming home. If they go to 2nd, I don't have an effect on the play. He complained that F1 hesitated to throw.
My response is, because his catcher was down almost on the ground and recovered to try to field his throw.