Flat-Footed Meaning

(idiomatic) unprepared to act

Example: having feet which are flat
  Bears are flat-footed animals.
(of humans) having the specific physical condition of flat feet
  They caught us flat-footed.
Holding firmly and maintaining a decision; to standing on one's ground.
  1892 Frank Millet: "I write in this way to urge you to be explicit and flat-footed in your wishes." Quoted in: 2003 Erik Larson, The Devil in the White City: Murder, Magic, and Madness at the Fair that Changed America, ISBN 0609608444, page 177.