Rules, Penalties, and Dead Hands:

What is a Dead Hand? 💀

A dead hand in American Mahjong refers to a situation where a player can no longer complete a valid hand. A player should not announce that their hand is dead. Even if a hand actually is dead, the player should continue to play defensively until someone else calls the hand dead. A player’s hand may go “dead” for a variety of reasons. It is not officially dead until another player verifies that Mahjong cannot be made, based on the tiles that are visible to all players. This can happen for several reasons:
⛔️ Incorrect Hand: If a player declares Mahjong with a hand that doesn't match the NMJL card, it is considered dead. Follow the card closely: Double-check the rules for the hand you're aiming for.
⛔️ Unfinished Hands: If a player fails to complete a hand by the end of the game, their hand is dead.
⛔️ Exposing Invalid Sets: If a player claims a discard to form a set that doesn’t follow the game’s rules, such as an invalid sequence or set, their hand becomes dead. (Ex: NEWS, a year grouping, or non identical tiles) Exception example: If someone exposes a pung but meant to expose a kong and they correct the exposure before discarding a tile that is allowed.
⛔️ Using Jokers improperly: Jokers can be used in most sets but not for Singles or Pairs.

Dead Hands ⚠️

Below are more specific scenarios in which a player can call another player’s dead hand.

Mahjong in error:
⚠️ When a player declares Mahjong in error and exposes the hand, the hand is declared a dead hand. The disqualified player discontinues picking and discarding. The other players continue to play. 
⚠️ No player should throw in or expose their own hand until the winner’s hand is verified.
⚠️ If a player calls Mahjong in error and the mistake is rectified immediately, before the hand is exposed or before other players expose or disturb their hands, the game continues without penalty.
⚠️ If a player declares Mahjong on a discard and places the discard on top of their rack or exposes tiles from their rack, and then finds they do not actually have Mahjong, they may change their declaration of Mahjong to a call for exposure. The game continues without penalty.
⚠️ If a player calls Mahjong in error and exposes part or all of the hand and all other hands are intact, the game continues but the declarer’s hand is “dead”. All tiles are returned to the rack. A Mahjong hand “intact” means that a player has not exposed tiles from their hand, other than the tiles that had been called for an exposure before the player had declared Mahjong in error. The dead hand discontinues play and does not pick and discard.
⚠️ When a player declares Mahjong in error and has been playing an exposed hand, the Jokers which were in the correctly called exposure(s) BEFORE the error, may be redeemed by any of the other players with a like tile, when it is their turn. However, at the point the hand becomes dead the part of the hand that was in error is returned to the rack. When a player declares Mahjong in error and has been playing a concealed hand, no Jokers may be redeemed, and the entire hand is returned to the sloped portion of the rack.
⚠️ If a player declares Mahjong in error and exposes part or all of their hand and all other hands are intact, the game continues, but the declarer’s hand is dead.
⚠️ If a tile is called and exposed resulting in Mahjong in error, the called tile must remain with the hand, even though another player wants to call the tile for an exposure. The tile becomes dead along with the rest of the hand. However, if another player wants the same tile for Mahjong, it may be called and used to complete the player’s hand for Mahjong.
⚠️ No such hand: If the exposed tiles do not represent any hand on the current Mahjong card, the hand is dead.
⚠️ If the player declares Mahjong while playing a concealed hand and the player has exposed tiles while playing a concealed hand, the hand is dead. If you expose on a concealed hand and realize it early in the game, you can pivot to another hand.

Other scenarios for dead hands:
☢️ If a player has too few or too many tiles, another player may call them dead.
☢️ If a player proceeds to make an invalid Joker exchange before the player picks and racks a tile or calls and exposes, the player’s hand is dead.
☢️ Unwinnable hand: The exposed tiles indicate that a player is attempting to make a Mahjong which requires either single tiles or a pair for completion. If three or more of the pair or four of the single needed tiles have already been discarded on the table or have been exposed by other players, the hand may be called dead.
☢️ If a player discards a tile before picking from the wall, the player’s hand is dead.
☢️ If a player picks out of turn the player’s hand is dead. If the tile is racked, it remains with the dead hand. If it is not racked, and another player immediate notices, it is placed back in the wall. If it is discarded, it is a dead tile and cannot be called except for Mahjong.
☢️ If a player picks from the wrong wall and a tile from the wrong wall is racked, the player who picked the tile now has a dead hand.
☢️ If a player picks from the wrong end of the wall, the player’s hand is dead, and the other players continue playing from the proper end. The tile remains in the dead hand.
☢️ If a player picks the wrong tile from the wall, the player's hand is dead.
☢️ If a player pushes out the wrong wall, and a tile from the wrong wall is picked, the player who picked the tile now has a dead hand. The tile remains in the dead hand. The game continues from the wrong wall and then proceeds from the correct wall.

Other rules:

📏 A Joker may never be passed during the Charleston. If it is, it must be given back.
 📏 A tile that has been discarded cannot be picked up and then used in a Joker exchange by another player.
📏 Once a tile has been named correctly or touches the table, it cannot be taken back to make an exchange for a Joker. Down is Down. A tile laid is a tile played.
📏 A discarded Joker can NEVER be picked up. It is a dead tile.