Question: What happens if someone accidentally picks a tile from the wall and places it on top of their rack and then takes other tiles from their rack to form an exposure?

Answer: If a player picks a tile from the wall and unintentionally places it on their rack, subsequently adding other tiles from their rack to create an exposure, their hand is considered dead. In this scenario, the player’s would cease playing.

Source: Letter from the National Mah Jongg League dated August 14, 2023