to confuse or upset someone for a short time by saying or doing something that they are not expecting: The question threw him off balance for a moment.

What does throw off balance mean?

to suddenly confuse or surprise someone. She was trying to behave as if his visit hadn't thrown her off balance.

Was caught off balance?

catch (one) off balance. To startle one; to come upon one unawares or unprepared. Usually used in the past tense. The security guard caught the thieves off balance.