flat-footed

Of an animal: having feet which are naturally flat; (specifically) of a horse: having hoofs with soles close to the ground.

Bears are flat-footed animals.

[T]here have ben novv of late, Serpents knovvn flat-footed like Geeſe.

Of a person: having the physical condition of flat feet (“a condition where the soles of the feet are in full contact with the ground, either because the arches have collapsed or because they never developed”).

[T]he volunteer from the 9th company was shot because he wouldn't advance and made the excuse that he had swollen legs and was flat-footed.

The figure came up and squatted flatfooted on his haunches next to Patsy. In the dim glow of starlight and streetlight he saw a wrinkled face and a silvery goatee.

Of a thing (especially (rail transport) a rail): having a flat base; flat-bottomed.

These rails, […] were of the "fish-bellied" pattern, but in practice, and as the demand increased, these were found troublesome to roll, and this difficulty led to the introduction of the flat-bottomed or "flat-footed" section of rail, combining a solid head with a flanged base.

Blunt and unsubtle; lacking finesse; clumsy.

The thing made a big stir in the town, too, and a good many come out flat-footed and said it was scandalous to separate the mother and the children that way.

Two Saudi battalions and a Qatari armored battalion were tasked with retaking the town, which they did in a slow and flat-footed fashion, supported by ample U.S. artillery and air power.

Unprepared, unready.

They were caught flat-footed when Clancy filed to enter the race.

To those who are younger, perhaps still building a career, I say to you, plan for it! No one should be caught flatfooted by the lengthening of middle age.