Calling a Mahjong Tile
A player may call the most recently discarded tile when it completes a legal grouping for an exposed hand or completes Mahjong.
To call a tile:
Clearly say “call” or name the completed group.
Take the most recent discard.
Place the called tile on top of your rack.
Add the matching tiles from your hand.
Display the complete exposure.
Discard one tile to finish your turn.
A discard cannot be called simply because it might be useful later. It must immediately complete a valid exposure. Concealed hands cannot call a discarded tile unless that tile completes Mahjong.