Bloody knuckles

Bloody knuckles is a game in which each player makes a fist with the thumb wrapped around the other fingers.

[2] Variations include simultaneous or alternate punching, and games in which the strike is the loser's punishment/winner's privilege.

Almost all ways of playing are dangerous, carrying the risk of injury, scarring, and damage to one's bones and hand.

[1]"Bloody knuckles" may refer to any game where the loser is punished: punched, slapped, or struck with an object.

Whichever player's touch causes the spinning coin to stop and fall down is considered the loser, and they must put their knuckles on the playing surface.

Then, the winner puts their thumb on the coin and forcefully pushes it across the table onto the loser's exposed knuckles.