Ran into a sitch the other day during a game. B18 is in front of A30 with his back to the thrown ball and his arms raised towards A30's face. A30 pushed off on B18 to make the catch and I called Off PI, after the play the BJ said he didn't throw his flag because he thought I was calling face guarding on the defense.

Is this def PI and which rule definition covers this?

You can find a reference for face guarding in the casebook

7.5.10 SITUATION C: A1 or B1 is in a position where he might catch or intercept a forward pass beyond the neutral zone. An opponent, who is in the vicinity, turns his back to the ball. The opponent directs his attention to A1 or B1 and waves his arms to block the vision of the potential receiver or interceptor. RULING: Hindering an opponent's vision without making an attempt to catch, intercept or bat the ball, is pass interference even though no contact was made. This is the only situation in which there may be pass interference without contact.

James - Thanks for the reference. We probably should of had offsetting penalties on this play.

double foul
 

Moreover, why didn't the B drop a flag? Then you could've gotten together and decide what the final call was going to be.

Officials should not assume another official will/will not make a call