Quick answer
A concealed hand, marked C on the National Mah Jongg League card, must be built entirely in your own rack. You may not call a discard for an exposure. The one exception is the tile that completes the hand, which you may call from a discard to declare mahjong. Exposing a set for a concealed hand makes the hand dead.
Next to every line on the League card is an X or a C, and a C changes how you can play that hand from the Charleston on. Here is what a concealed hand is, what you may and may not call, how jokers work in one, what happens after a wrong mahjong call, and how it scores, with the rule behind each answer.
What is a concealed hand?
Next to every line, the League card prints an X or a C along with the hand's value. X means the hand may be exposed. C means it must be concealed, built entirely in your own rack, and the only tile you may take from a discard is the one that completes it.
Everything else has to come from the wall, the Charleston or the courtesy pass. None of your sets go face-up on your rack until you declare mahjong, so the table sees none of them until the hand is complete.
The X lines are the exposed hands. On those you may call discards, lay the sets face-up on your rack and keep building. A C line takes that option away, so every tile but the last has to reach you some other way.
What can you call on a concealed hand?
Only the winning tile. If a discard completes your concealed hand, you may call it and declare mahjong. That tile may even complete a pair or a single, which no discard may be called for at any other point in the game.
Any other call means exposing a set. You claim the tile, place it on top of your rack with the tiles it goes with, and the set stays face-up for the rest of the hand. Once you have called a discard for an exposure, the concealed lines are gone for that hand.
Calling a set while you are going for a concealed line ends that line. If your exposures then fit no exposed line on the card, the hand is dead, which the dead-hand guide covers in full.
So changing direction only runs one way. Before you have called anything, you can move from a concealed line to an exposed one at any time. After an exposure, you cannot move back.
How do jokers work in a concealed hand?
Yes, in the same places as in any other hand. A joker can stand in for a tile in a pung, kong or quint, and never in a pair or a single. On a line made only of pairs and singles, no joker can be used at all.
Your own jokers are safe. A joker can only be redeemed from an exposure, and a concealed hand has none, so nobody can trade a tile for a joker in your rack.
You can still redeem other players' jokers. On your turn, after you pick from the wall, you may swap the tile a joker stands for out of your rack for that joker in an opponent's exposure, and use the joker in your own concealed sets.
What if you call mahjong in error on a concealed hand?
Under the League's tournament rules, calling mahjong in error costs nothing by itself. The penalty comes when tiles are shown. A player who calls mahjong in error and displays or exposes tiles from the hand is dead and scores zero for that hand.
A concealed hand has a rule of its own. If it is wrongly exposed for mahjong, the tiles go back into the rack, nobody may redeem its jokers, and the player stops picking and discarding for the rest of the hand.
An exposed hand is handled differently. Its exposures made before the error stay on top of the rack, and any player may redeem the jokers in them on their turn. A wrongly exposed concealed hand gives none of its jokers to the table.
The tournament rules note that social and home games may differ, so check how your own table handles a wrong call.
How does a concealed hand score?
By the value printed next to it on the card, the same as every other line. The League sets each hand's value, and we never reprint the card's values here, so check your own copy.
The League's tournament rules add no bonus for being concealed. Every hand earns the same two bonuses, ten points for picking your own winning tile and twenty for using no jokers, and the Singles and Pairs hands get no joker bonus.
Being concealed does change one penalty. The player who throws the winning tile loses ten points when the winner has no exposures or one, twenty when the winner has two and twenty-five when the winner has three. A concealed hand has no exposures, so whoever throws its winning tile loses ten.
For home games, the scoring guide covers who pays what when a hand is won.
What is a fully concealed hand?
The term comes from the Chinese competition rules known as MCR, the Mahjong Competition Rules. There, concealment earns points of its own. A Concealed Hand, with no melded sets and won on a discard, scores 2 points. A Fully Concealed Hand, with no melded sets and won by drawing the last tile yourself, scores 4.
American mahjong works the other way round. Concealment is a requirement the card prints on certain lines, not a bonus you choose to earn. Under the League's tournament rules, playing an X line without calling anything earns nothing extra, and a C line allows no exposures at all.
What does a concealed line ask of you at the table?
Every tile but the last has to come from the wall, the Charleston or the courtesy pass. Discards that would complete a set for you go by, because calling one ends the concealed line.
It also shows the table nothing. With no exposures on your rack, opponents have only your discards to read, which is the other side of giving up calls.
Whether a concealed line suits a given rack depends on the tiles in it, and there is no rule that settles it. Reading the rack you were dealt is where that decision starts.
Put it into practice
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