Deadball PF vs Roughing the Passer - help

[Theisey]

Jasons answer for NCAA would apply for NF. The passer is no longer a passer at this point as the pass has ended. You say the defender had contacted the QB while he was in his throwing motion. Be hard pressed to call roughing at that point.

Go with a dead-ball personal foul. That's really all you can do. Sure this is not going to be an auto-1st down and of course the team-A coach will be questioning you on it.
It will be even harder to explain if this were a 4th down play and now team-B is going to snap the ball but you would be correct.