stumble, fall down, wrestle
跤 centers on losing one's footing and falling, or the physical struggle of wrestling where stumbling and grappling are central.
跤 combines 足 (foot) with 交, which likely contributes the sound and suggests crossing or interlocking legs, as in stumbling or wrestling.
The left side is 足 (foot), and the right side 交 looks like crossed legs. Picture feet getting tangled and causing a stumble, or two wrestlers' legs interlocking as they grapple.
For コウ, imagine a wrestler stumbling and letting out a loud 'KOH!' as they fall: KOH -> コウ, and the tangled feet cause the stumble.