Be caught flat-footed phrase
To be startled or surprised while unprepared; to be put in a difficult or disadvantageous situation when something happens which one does not expect
My roommate was caught flat-footed as soon as I entered the room. It made me smell something fishy.
I was caught flat-footed by her tough question.
Many companies were caught flat-footed by the recent recession.
One dishonest person can guess what another dishonest person might do
To scare someone.
If you say that you feel one's collar, you mean that you arrest him legally.
To surprise someone.
The verb "be" should be conjugated according to its tense.