Farewell to Arms

As this enchantment enters, choose a hand attached to an opponent's arm. When the chosen hand isn't behind its owner's back, sacrifice this enchantment. If you do, that player discards their hand . . . of cards. (The lawyers wouldn't let us do it the other way.)

From Magic: The Gathering.

Open the interactive version on https://mythscribe.cloud/app/tcg/cards/cms6o9wdi6k61pb1hse97zkc9.