noun
yakyūken; strip rock-paper-scissors
A game similar to strip poker, but using rock-paper-scissors (janken) instead of cards. The loser removes an article of clothing. Often associated with drinking parties or comedic contexts.
合宿の夜、みんなで野球拳をして盛り上がった。
On the night of the training camp, we all got excited playing yakyūken.
テレビのバラエティ番組で野球拳を見たことがある。
I've seen yakyūken on a TV variety show.
脱衣麻雀 is strip mahjong, a similar concept but using mahjong instead of rock-paper-scissors.
Literally 'baseball fist', but the name is misleading. The origin is uncertain; it may derive from a chant used in the game or from an old baseball-themed variant of rock-paper-scissors.