infield fly and an interference

[okla21fan]

High School in Texas NFSHS (but ASA rule set if different would be great too)

R1 and 2nd, R2 on 1st with 1 one out. F6 is playing inside the base path. B3 hits a flair (not more than 12 to 15 high and a weak hit) fly ball to towards and past F6 who turns and runs back to field the flair. R1 breaks on contact and and ultimately collides with F6 (neither player saw the other nor there was intent, just classic DMR) BU calls INT on R1 at contact and kills the play. (R1 is 2nd out of inning)

here is the question for ruling:

1) PU has not called an IF prior to killing the ball for the INT by the BU.

2) PU did call IF prior to IF and BU killing the the play.

I saw this play, and questioned the normal effort to rule an IF, but since there was contact by R1, I could see why the 'bubble' of normal effort could increase. (ruling on the field was R1 was out for the INT, and B4 was out for the IF. 3 outs, inning over)

My question, Does INT negate an IF before the IF is actually called? (at the apex of the flight of the batted ball) Does an IF happen at the point of contact with the bat...(although usually not ruled till moments later)

I could not find a case play similar to this (2009 case book)

Thanks!