flat-footed
flat-footed {adj.}, {informal}
1. Straightforward; forthright; direct; outright.
The governor issued a flat-footed denial of the accusation.
He came out flat-footed against the idea.
2. Not ready; not prepared; — usually used with "catch".
The teacher's question caught Tim flat-footed.
Unexpected company at lunch time caught Mrs. Green flat-footed.
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Source: A Dictionary of American Idioms