A pressor field was a ship-generated energy wave that covered a vessel which protected it from attack. Despite this, it can be overwhelmed.
The Transformers cartoon
A Quintesson cruiser, in its attempt to locate a Quintesson Journal, was uncovered by Superion whose power would have destroyed the ship. In order to protect themselves, the Quintessons activated a pressor field which held back the giant Autobot until he fired his shoulder cannon that nullified the field.