leather arm guard
鞲 refers to a leather arm guard, a protective piece worn on the arm.
鞲 combines 革 (leather) with 冓, which likely contributes the sound. The character specifically denotes a leather arm guard.
The left side 革 means leather, and the right side 冓 looks like a framework or structure. Imagine a leather framework shaped to fit around the arm as a guard.
For コウ, picture a leather arm guard worn by a coach (コウチ) during practice: coach -> コウ, and the guard protects the arm.