to bend the wrist, come off, be broken
捥 centers on a forceful bending or twisting action that causes something to come off or break, especially at a joint like the wrist.
捥 combines 扌 (hand) with 宛, which likely contributes the sound and may relate to bending or twisting. The exact historical development is uncertain.
The hand radical 扌 beside 宛 suggests a hand forcefully twisting something until it bends, comes off, or breaks.
For ワン, imagine a wrist bending back with a sharp 'wan' sound as it breaks: wan -> ワン.