Same answer here from me as I gave on Facebook.
The booby traps must be set up before deployment, so it cannot be deployed on top of anyone. It gets deployed before any fighters do.
It only possibly goes off if they move into/in range. If they stand still and shoot at it, it (most often) won’t go off. Deploying isn’t moving. The Booby Trap rules say it is triggered by movement within 2”.
Separately, sinking enough credits into covering the entirety of an opponent’s deployment zone in booby traps is … an interesting choice. Not likely a successful one in the long run.
The Trap turns out to be the one scenario where at least one model has to deploy at the centre of the table, and if the fighter’s base is wider than a half inch (13mm), no other fighter will need to be within two and a half inches of the booby trap in question. So it MIGHT go off if that one fighter moves, and if it does, will hit that one fighter the defender chose to place next to the trap.