I think that’s right. It might vary between designs, but the trigger should fully disengage the windlass from the catapult arm when the piece fires. The windlass wouldn’t spin. The smaller catapults Romans made (Scorpion bolt-throwers, etc.) seem to have had the handles fixed on to the crank. Those handles were clear of the ground, but it suggests to me that the bar/spike on the larger catapult could be left in the hole. If I was the crew boss for the piece, I would probably still have a crewman remove it and stand clear when firing, so that it isn’t in the way when starting to prepare for the next shot (and it wouldn’t be flung out or broken it there is a malfunction...)