When is a player committed to taking a discard from the table?

When calling a discarded tile, a player is committed to the call if they have either exposed tiles from their hand on the top part of their rack (prior to picking up the discarded tile) or placed the called tile on the top part of their rack. If they have picked up the discarded tile and still have it in their hand, but haven’t exposed any tiles or placed the discarded tile on their rack, they can put the tile back on the table.