If a player accidentally drops a card from their hand face-up onto the battlefield during hand shuffling, has that card been legally played?

Ruling: The card has not been legally played and should be returned to the player's hand. The player has not expressed intent to play the unit, has not tapped runes to pay the cost, and has not communicated that they were playing a unit.

Sequence:

• Player A drops the card accidentally onto the battlefield
• Judge determines no intent was expressed to play the unit
• Card is returned to Player A's hand
• Player A is instructed to be more careful

Nuances:

• Showing a card from hand to an opponent is a legal action in Riftbound (even if accidental), so no game play error occurs for revealing the card
• No new information was gained by the player, so rewinding is appropriate under the rules
• If a player repeatedly "accidentally" drops cards to gain information about opponent reactions, this could constitute angle shooting
• If the situation is unclear or disputed, it should be treated as a communication error and rewound to before any unclear communication