Calling and Exposing in American Mahjong: When, How, and When Not To

What you can call, and what you cannot

You may call a discard to complete a pung (three of a kind), a kong (four), or a quint where the card calls for five. You may not call a discard to complete a pair, with one exception. You may call for the pair that completes your entire hand, which is the winning call. The same limit covers a group of different tiles, such as NEWS or the year. You may not call a discard into one unless that tile completes your entire hand. There is no calling for runs in American Mahjong, which matters if you learned Chinese mahjong first, where runs can be called.

Any player may call any discard regardless of seating position, unlike Chinese mahjong where seat order restricts some calls. If two players call the same tile, a call to win beats a call for an exposure. If both call for the same thing, the player next in turn after the discarder gets it, unless the other caller has already started to expose tiles for the claim.

The mechanics

Say the word out loud. League rules require a claim to be spoken, and a player who does not speak up loses the right to the tile. The window stays open until the next player racks the tile they drew or discards. The next player touching a wall tile does not close it for anyone else, though it does close it for that player, whose turn has started and who must now take the tile. Holding the drawn tile, or setting it on top of the rack or in front of it, does not close it either. Racked means placed in the rack among the player's own tiles. Once another discard covers the tile, nobody can claim it for anything, including mahjong.

Speed still matters. The sanctioned tournament rules ask the next player to pause for a second between picking and racking so the table has a fair chance to call. That pause is a courtesy, not a time limit. The window lasts as long as the next player takes to rack or discard, and at a quick table that can be about a second.

When your call is accepted, take the tile, then lay the complete set face up on top of your rack, including the tiles from your own hand. Then discard, because you have taken a tile and must give one back. Play resumes to your right, which means calling can skip other players entirely.

The claimed tile goes into the exposure on top of the rack, in view of the table, never into the rack itself. The sanctioned tournament rules make a hand dead for putting a claimed discard in the rack, because the other players have to be able to see that the tile exposed is the tile that was thrown.

Changing your mind, and fixing a mistake

You may take back a claim with no penalty, as long as you have not touched the tile, have not exposed it, and have not exposed any tiles from your hand. Past that point the tile is committed. A claimed tile you have touched must go into an exposure.

An exposure made in error can be fixed while it is still your turn. Under the sanctioned tournament rules you may change a pung to a kong or a quint, or back again, until you discard, and that discard ends your turn and fixes the exposure.

A discard named wrongly has its own rule. If someone claims it for an exposure and the discarder holds the tile they named, the discarder must put the named tile out in its place. If they do not hold it, the discard counts as the tile it really is and play goes on. A mis-named tile can still be claimed for mahjong, and in tournament play the discarder loses 25 points for giving an opponent the win with it.

If you claim a mis-named tile and expose tiles from your hand before checking it, you must still use the claimed tile in an exposure, rearranging your hand if you need to. If you cannot use it, your hand is dead. Look at the tile before any of your own tiles leave the rack.

What an exposure is, and when one is invalid

An exposure is a set you lay face up on top of your rack after calling a discard. It holds the tile you called and the matching tiles or jokers from your hand, and it stays there, in view of the table, for the rest of the hand.

An exposure is invalid when it cannot be part of any hand on this year's card. The set may match no line at all, or it may not combine with the sets you have already exposed into any single line. Lines marked C on the card must stay concealed, so a set that fits only those lines is invalid too. The sanctioned tournament rules call this an incorrect exposure.

You can fix an incorrect exposure on the turn you made it. Until you discard, you may change the set, a pung to a kong or a quint or back again, and move tiles on and off the top of your rack. Once you discard, the exposure stands. If your exposures then fit no line on the card, your hand is dead. You stop picking and discarding for the rest of the hand, and you still pay the winner. Other players can still redeem a joker in an exposure you made correctly before your hand died, but not a joker in the exposure that made it dead.

Jokers in exposed sets

Jokers may stand in for any tile inside a pung, kong, or quint, but never in a pair and never as a singleton. This is why calling matters so much for joker-heavy hands. A joker can only be used in a set of three or more, so hands built on pairs give your jokers nowhere to go.

Once a joker sits in an exposed set, any player may redeem it on their turn by offering the real tile it represents, after they have drawn from the wall or laid down the exposure they called. A player may not take an exposed joker to finish the exposure they are making with a discard they just claimed. Redemption is a genuine risk of exposing early. A joker safely hidden in your rack cannot be taken from you.

Calling a discarded joker

No, not for an exposure and not for mahjong. A discarded joker is dead under League rules, so nobody can call it. It also covers the tile thrown before it, and once a discard is covered nobody can claim it either.

That is why every exposed set holds at least one natural tile, the discard that was called to make it. A set made only of jokers is never exposed during play. It shows only when a player lays down a winning hand.

Adding to an exposure on a later turn

No. The rules printed on the back of the League's card allow a player to change an exposure only until that player discards. The discard that ends the turn you exposed on fixes the set for the rest of the hand. If you exposed a pung of five dots and the fourth five dot is discarded two turns later, you cannot call it to make a kong. If you draw the fourth one yourself, it cannot go onto the pung either.

Chinese and Hong Kong rules let a player add a drawn fourth tile to an exposed pung on a later turn. American Mahjong does not.

Jokers follow the same rule. The League has ruled, in a 2019 letter and in a bulletin, that once an exposure has been made, a player cannot start a joker exchange and add that joker to it. The card does not print that ruling, and the mah-jongg author Tom Sloper reports it. You can still exchange a joker out of your own exposure for the natural tile it stands for, which leaves the set the same size.

So settle the size of a set before you lay it down. Check the card line you are building. If it needs a kong in that spot, expose all four tiles when you call, using matching tiles and jokers from your hand. A pung already on the rack cannot become a kong later.

What calling actually costs

Every exposure is free information for three opponents. When you lay down three of a number, everyone at the table can rule out every line that cannot hold that set, and they can stop discarding what you need. Any of them can act on it from their very next discard.

The tile goes to you, and the information goes to all three opponents. So the question before every call is whether the tile speeds you up more than the table slows you down once it stops discarding what you need.

When to call, and when to sit on your hands

Call when the tile completes a set you were always going to need, when you are already committed to one hand with no realistic alternative, or when you are close enough to the end that the information no longer has time to hurt you. A late exposure still tells the table what you need, but it leaves them fewer turns to act on it.

Stay quiet when you are still deciding between two directions, when the call would lock you out of a better hand, when your hand needs a concealed line, or when the set you would expose is the only thing telling opponents which suit you want. Early exposures are the most expensive ones, because they give the table the most time to use them.

Before calling, name to yourself the exact card line you are building toward. If you cannot name it, you are not ready to expose.