Playing an Interrupt is not firing a weapon; it's playing an Interrupt. Like I said before, players alternate opportunities for actions in the weapons segment. The player who initiates gets the first chance to perform an action. He could fire a weapon, play an Interrupt, or do many other things as the rules allow. Once he finishes performing his first action, then the opponent gets a chance to do the same thing. I really can't see why that is so hard to understand.