roll up sleeves, fight bare fist
揕 centers on preparing for direct physical confrontation: rolling up sleeves to free the hands and fighting with bare fists.
揕 combines 扌 (hand) with 甚, which likely contributes the sound and may relate to the idea of extreme or intense action. The exact historical development is uncertain.
The hand radical 扌 beside 甚 suggests using hands in an intense way: rolling up sleeves to fight bare-fisted.
For チン, imagine a fighter rolling up sleeves and landing a sharp chin punch: chin -> チン, and the hand 扌 delivers the bare-fist blow.