Challenges

Facing a play, the opponent may issue a challenge, call "hold", or accept the turn (3.10.1, 3.10.5, 3.11); The turn is accepted if the opponent neither holds nor challenges before the player's replacement tile reaches the rack (3.10.1(b)); Accepting a turn waives the right to challenge it (3.10.1...

Send this to your friend — argument over.