How would you handle?

[MD Longhorn]

Working the wing last night. Screen pass set up to my side. We'd had a major problem with this team holding on the screen passes all night, so I was concentrating on them. Three of them were across the line (normal), and when the ball is thrown I'm looking at them. The ball zips past me at my ankles (I'm right on the line at this point) incomplete. I whistle and signal incomplete and watch for a second for late hits, etc, then turn for the ball.

The back of my brain starts tickling --- ineligible downfield? Was that ball still in the air when it passed me? Was it tipped? About 2 seconds later the same thing dawns on the coaches on my side... "Ineligible!!! Ineligible!!!" (Side note - I HATE dropping the hanky after a coach asks for one, as a matter of principle).

I went in, asked R if the ball was tipped, and asked U (who had the best angle) if the ball landed across the line. After getting the right answers, I tell R I have ineligibles downfield and drop the flag.

How would you have handled? I KNOW I should have dropped the flag immediately ... but having failed in that - do you drop it when first realized you may have missed it? When the coaches started yelling? Or when I did - after confirming the facts?