be caught off (one's) guard
To be taken by surprise; to be caught when one is vulnerable, careless, or inattentive. We'll wait until he's caught off guard, and then we'll take him and his company for all they're worth! Don't be caught off your guard. There are a lot of suspicious characters around here. Terry hadn't prepared anything to say at the reception, so he was caught off his guard when they asked him to say a few words.
Farlex Dictionary of Idioms. © 2024 Farlex, Inc, all rights reserved.