Umpire interference?

[mbyron]

Everyone's familiar with the umpire interference (UI) where the BU in the infield gets hit by a batted ball which an infielder could have a play on. We kill it, award BR 1B, and other runners return unless forced.

But there's another kind of UI: when PU interferes with F2's attempt to retire a runner who's stealing, we kill it and send the runner back.

Had a situation last weekend that, I now think, probably should have been UI. I was BU.

R2 stealing, outs don't matter. F2 comes up, steps on umpire's foot, throw sails into LF. (This is the same play I posted in another thread, where F5 landed on the runner and I called OBS, but that's another story.)

As we discussed the call I had made on F5, my partner mentioned that the throw was so bad because F2 had stepped on his foot. I asked him whether that wasn't UI (and explained the rule to him). He decided not to call it, since he hadn't moved: F2 had simply put his foot in the wrong place.

This was clearly his call, and he understood the rule, so I didn't argue with him. If I had been PU, I probably would have ruled UI on myself, on the grounds that, even if I'm in my usual position, F2 should have an unhindered play on the runner stealing.

I don't know the enforcement of this rule, and don't have the MLBUM. I would appreciate any guidance.