Commitment to Calling a Discard (Article ID 21)
Abstract: A commitment to a called tile occurs when a player either exposes tiles on the flat part of their rack, placed the called tile on the flat part of their rack or placed the called tile on the sloping part of their rack along with their other tiles. This ruling is not found in Mah Jongg Made Easy.
Question from a player: I called a tile and picked it up but decided I don’t want it. I have not exposed any tiles from my hand. Can I change my mind and put the tile back on the table?
Answer from the league: “Saying “call” or picking up a called tile is not a commitment and a player may change their mind. A player is committed to a call once tiles have been exposed on the rack or the called tile has been placed on or in the rack.”
Source: National Mah Jongg League Bulletin Q&A 2020
Other answers from the NMJL:
“Once a player starts to make an exposure, her commitment is made.”
“You are committed to a call when you have either exposed tiles from your hand or placed the called tile on top of your rack.”
Source for other answers: National Mah Jongg League Bulletin (1997 page 6, 2015, 2017) https://nationalmahjonggleague.org