Question: During my game today, a player called a discarded tile at the same time another player picked their tile from the wall and racked it. What happens when this occurs?

Answer: When there is a simultaneous pick from the wall and rack at the same time another player calls a tile, preference is given to the player who called the tile.  The only exception is if the picked tile is for Mah Jongg as Mah Jongg always trumps. 

Source: National Mah Jongg League Bulletin Q&A (2020) and a call to the NMJL by a player on 12/20/2023