Used after verbs to describe the manner of action (‘He landed flat-footed’) and figuratively to mean ‘squarely, bluntly’.
Definitions
In a flat-footed manner; flat on the feet or squarely, without hesitation or finesse. He landed flat-footed on the mat and felt a sharp jolt run up his legs.
Bluntly or straightforwardly, without equivocation. She told him flat-footed that the project had failed.