Flat-footed

[flat-foo t-id] /ˈflætˈfʊt ɪd/

adjective
1.
having .
2.
taking or showing an uncompromising stand in a matter; firm and explicit:
a flatfooted denial.
3.
clumsy or plodding; maladroit:
flatfooted writing.
Idioms
4.
catch one flatfooted, to catch one unprepared; surprise:
The amount of the bill caught us flatfooted.
/ˌflætˈfʊtɪd/
adjective
1.
having flatfoot
2.
(Brit, informal)

3.
(informal) off guard or unawares (often in the phrase catch flat-footed)
adj.

c.1600, “with flat feet;” meaning “unprepared” is from 1912, U.S. baseball slang, on notion of “not on one’s toes;” earlier in U.S. colloquial use it meant “straightforwardly, downright” (1828), from notion of “standing firmly.”

adjective

Unprepared; surprised •Usu in the phrase catch someone flatfooted: He just stood there flatfooted and watched it roll in (1912+ Baseball)

adverb

Straightforwardly; without ceremony: If they were going to turn it down, they would have just flatfooted done it (1828+)
see: caught flat-footed