take (one) off guard(redirected from take someone off guard)
take (one) off guard
To engage, take advantage of, or seize upon one when one is not especially careful, vigilant, or prepared for danger or surprises. He's got a lot of tricky moves, so make sure he doesn't take you off guard! The soldiers moved in quickly, hoping to take the enemy troops off guard. I think I took him off guard when I told him I was resigning.