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.
Once a player names or discards a tile he cannot change his mind and discard a different tile.
When a player calls a tile and places it on the flat part of their rack or exposes tiles from their rack, they are committed to taking that discard.
A player cannot reverse the action once a Joker placing with a natural tile.
Once a player lifts or moves a tile they are committed to taking their pick from the wall.