Quick answer
The first Charleston, passing three tiles right, across and left, is mandatory, unless East is dealt a complete hand. Any one player may stop the second Charleston without a vote or a reason, by saying so before anyone racks a tile from its first pass. The courtesy pass across is still available either way.
Somebody at the table says 'stop' and not everyone is sure whether they were allowed to. Here is the rule, the timing, the strategy behind stopping or not stopping, and the two disputes it causes.
The rule
The first Charleston, three passes of three tiles (right, across, left), is mandatory. The one exception in the sanctioned tournament rules is East being dealt a complete hand, all fourteen tiles already a hand on the card, and East may stop the passing there. The second Charleston (left, across, right) is optional, and any single player may stop it. It does not need a vote, and nobody has to give a reason.
The optional courtesy pass, an exchange of up to three tiles with the player across from you, is available after the Charleston whether or not the second round was played. Each of you names a number from zero to three and you exchange the smaller, so either of you can decline it.
When to say it
The decision belongs to the moment between the end of the first Charleston and the start of the second. Say 'stop' or 'no second Charleston' out loud before anyone has passed a tile of the second round. Under the sanctioned tournament rules a late stop still counts while nobody has racked a tile from the second Charleston's first pass. That pass is called back and the passing ends. Once any player has racked one of those tiles, the second Charleston runs to the end. A glance at the tiles is not racking them.
Say it clearly and once. At tables that play fast, a mumbled stop is the beginning of an argument. The ruling turns on racking, not passing, so a stop called while the passed tiles are still face down on the table holds.
Why a player stops
Because their hand is settled. After the first Charleston a player who already has two or three sets and a pair prospect has little to gain from passing three more tiles three more times and quite a lot to lose, since every pass forces them to give up something.
Because a full second Charleston would tell the table too much. Passing is information, and a player who keeps passing lone winds and dragons is showing everybody what they are not building.
Why you should usually let it run
If your hand is not settled, the second Charleston is nine more tiles of chances at the pair or the set you need, and the tiles you pass away are ones you were not using. Stopping too early, out of fear of passing something useful, leaves you with a deal that never moved.
The second Charleston also gives you information about everyone else. Watch what each pass brings you, and you learn which directions your neighbours have given up, which is exactly what you need to know before the first discard.
What happens after a stop
Play proceeds to the courtesy pass, if the two players across from each other want one, and then to East's first discard. Nothing else changes. There is no penalty, no extra draw, and no reshuffle.
A stop is not a tell in itself. Any player may stop, whatever their hand, so a stop does not always mean a made hand. Read it together with everything else, not on its own.
The two disputes and how to settle them
The first dispute is a stop called after the first tiles of the second Charleston have been passed. If nobody has racked any of those tiles, the stop holds and the pass is called back. If anyone has racked one, it is too late and the round continues. The second is a player trying to stop the first Charleston, or to skip one pass of it. That is not allowed, unless that player is East holding a complete hand from the deal. Otherwise the first Charleston is played in full at every four-player table that follows the League's rules.
If your group plays a house rule, such as stopping the second Charleston mid-round when everyone agrees, agree it before the first deal, and treat it as a table rule rather than the game's rule when you sit at a new table.
Put it into practice
New to the game? Start the course at Lesson 1, Meet the Tiles. The first three lessons are free and need no account.
Already play? Have the coach read a real dealt hand for you, free. It names the direction the hand goes for, what to keep, what to pass, and the reasoning behind each call.
Whether to stop the Charleston is the same question as whether your hand is settled. Mei, our AI coach, reads a dealt hand and says which direction leads, what the backup is, and whether the hand has committed yet.