An Even Number of Umpires Making the Call

[CecilOne]

Originally Posted by MD Longhorn

Based on these words alone, this is not INT.

By your own words, at the moment the batter-runner moved backward, F3 was attempting a throw, not a tag. "Delaying her approach to 1B" is completely legal (heck ... it's good baserunning).

Looks like the crux is " the BR had moved back with the throw"; which seems to mean a tag was not being attempted.

Back to the mechanics question, I believe the BU has primary responsible for most of BR; but the OP implies pretty close to HP, like a swipe tag in the first half of HP to 1st is usually the PU call.
Of course, as said " see it, call it" for INT or OBS.

BTW, not necessarily a NCAA answer.