In anticipation of next season's Saki - The Nationals series, which Crunchyroll has recently announced that they'll be streaming, I made my way through both the original Saki series and the spinoff/sequel Saki: Episode of Side-A. It's an incredibly addicting series, as exciting as any good sports anime, even if you might not think it would be for a game like mahjong. If you've seen any of the show already, you probably already know whether or not you'll be watching the Nationals arc.
But if you're curious about the show and want to check it out (and both the original series and Side-A are available for streaming on Crunchyroll already), but are hesitant because you don't know anything about Japanese mahjong, this post will be a basic introduction to the game. (And if you're not interested at all in the show itself, but are interested in the game… well, this post is for you, too.)
Japanese Mahjong can get quite confusing, so this post will focus only on some basic aspects of the game, enough to understand what's going on if you decide to go on and watch Saki afterwards.
Mahjong consists of several tiles, including three suits--circles, bamboo, and characters--with numbers 1-9 in each suit, as well as other tiles that are grouped in non-numeric ways. Of any given tile, there are four of that tile total in the entire mahjong set.
A mahjong game is officially played by four players (although two- and three-player variations exist). Games can vary in length by the number of rounds, typically indicated by a direction (usually East or South, with East always being the first round); each round consists of at least four hands, such that each player gets a chance to be the dealer once (or more) per round. One will typically see short games consisting of a single East round, slightly longer games with an East and South round (which is called one hanchan), and "full" games of two sets of East and South rounds (two hanchan).
During any given hand, each player starts with a hand of 13 tiles. Then, starting from the dealer and going counter-clockwise, each player draws one tile and discards one tile (unless someone decides to steal a tile someone else has discarded; more on that later). The goal is to complete a hand, including the tile drawn (or stolen), that consists of 4 sets of 3 (or 4) and one extra pair of matching tiles. Sets can either consist of three (or four) of the same tile, or a run of three consecutive numbers in the same suit. In addition, the hand must fulfill a certain condition, called yaku, in order to be a winning hand. There are a large variety of yaku, many based on the nature of the hand (such as having only numbers 2-8 or having certain non-suited tiles).
It's important to know that while it is possible to make a set of four identical tiles, called a kan (or kong), the fourth tile is actually not a part of your hand; if you make a kan, you must declare it and then draw another tile, albeit from a part of the wall that is specifically reserved for such draws (called the dead wall), among other things, and is not drawn from normally.
To help build a winning hand, players can choose to steal the most recently discarded tile instead of drawing one. There are four times a tile can be stolen, with some rules on each.
A pon (or pung) consists of stealing a tile in order to complete a set of three matching tiles. A pon can be called even if it is not your turn; in fact, if this call is made, the game will continue from the player that made the call.
A player can also steal to create a kan, with the same rule of having to draw an additional tile from the dead wall afterwards.
A chi (or chow) consists of stealing a tile in order to complete a run of three consecutive numbers in the same suit. Unlike pon and kan, a chi call can only be made if it would normally be your turn to draw, stealing only from the player on your left; furthermore, pon and kan take priority over chi.
When making any of the above steals, the set that is completed with the stolen tile must be shown face-up and placed to the side. Furthermore, this turns your hand from a "closed" or "concealed" hand to an "open" hand, which is important as this can potentially drop the point value of your hand or even make your hand no longer fulfill yaku conditions.
Finally, if a tile someone discards allows you to make a complete, winning hand (regardless of if it completes a set of same tiles, a sequence, or finishes the extra pair), you can steal it and end the hand, regardless of whose turn it is. This is called ron. It takes priority over any other kind of steal. More on this later.
Winning points with a winning hand
Mahjong is ultimately a game of points--specifically, of taking points from other players. A winning hand is worth a certain number of points, which are then taken from other players. It's worth noting that the dealer will win more points from the same hand than a non-dealer would, but will lose more points from an opponent's winning hand than non-dealers would.
Furthermore, if a dealer wins a hand, the game moves on to a bonus hand with the players in the same position, and with additional points at stake; if the dealer continues winning, the game continues into further bonus hands, with more bonus points at stake, until someone else wins.
The point value of a winning hand is determined by the base points of the hand (determined by various factors), as well as the han value of the player's hand. Each yaku has its own han value, and if multiple yaku can apply to a hand, those han will stack. Han can massively increase a hand's value; lower-value hands have their point values doubled by one additional han, while hands with multiple han are worth large number of points depending on how many han there are. (Terms such as mangan or baiman refer to a set number of points awarded for a certain number of han.)
(There are some hands that are so rare that they are automatically worth the maximum of 13 han and the maximum total point value of 32,000 (48,000 if you are the dealer); these killer hands are called yakuman.)
Dora are tiles that add one han each, although they cannot count as yaku. At the beginning of each hand, a tile from the dead wall is flipped over as a dora indicator; it's not the tile shown itself that is the dora tile, but the next one in sequence in that tile's suit or grouping. Games can optionally include special red "5" tiles that are also automatically one dora. Furthermore, if a kan is called, an additional dora indicator tile is flipped over for more possible dora. And if a player wins by riichi (more on this later), the tiles under the dora indicator also become dora indicators.
How to win (or lose) a hand
There are two ways to win a hand. The first way is by tsumo, or winning from a tile drawn normally. If you choose to win by tsumo (you can choose to not declare a win yet to try to build a better hand), you take points from all the other players, with the dealer paying about twice as much as the non-dealers pay (if the dealer wins this way, everyone pays the dealer equally).
The other way to win is by the aforementioned ron, or by stealing another player's discard. If you choose to win this way, the player you steal from must pay the entire point value of your hand. (Naturally, while this is a cool way to win a hand, it is also the worst way to lose a hand to someone else, hence why playing defensively to avoid discarding a tile that someone else can use to complete a hand is an important part of mahjong strategy.)
Tenpai and riichi
Tenpai is the state of your hand being one tile away from being a winning hand. Expect to hear a lot about players being in tenpai or some number of tiles away from tenpai. Once in tenpai, the tiles needed to complete the winning hand are called waits.
If a player is in tenpai, and has a "closed" hand (i.e. no steals have been made), she can declare riichi. Riichi is a type of yaku, so it can be declared with any combination of 4 sets of three plus an extra pair, even if it does not otherwise have any yaku. Riichi is declared by placing a 1,000-point stick on the table, which goes to the next person to win a hand (and yes, that means you lose 1,000 points if someone else wins the hand) and discarding a tile sideways.
Once a player has declared riichi, she cannot change her hand; any tile that is drawn that does not complete her hand must be discarded. (The exception is if that tile can make a kan from an existing triple in her hand, with the caveat that doing so cannot change the tiles needed to win.) The player must wait until someone else discards a tile she needs, or she draws that tile herself.
Riichi can be dangerous since you no longer have control over your discards and it becomes easier for someone to call ron over a tile you discard. On the other hand, riichi adds one han to your hand's point value (and can add an additional han if you do so on your very first discarded tile, or if you complete your hand within one go-round), and turns any tiles underneath dora indicators into additional dora indicators, which can potentially increase the han value of a hand even more.
Some final notes
During mahjong games, you will frequently see dice being rolled. These dice determine who starts as dealer, as well as where in the wall of tiles players start drawing from, and where the dead wall is.
There are some additional way to get yaku/han, such as completing your hand with the extra tile drawn after making a kan, or by winning off the very last tile drawn in a hand (before reaching the dead wall).
In addition, there are some winning hands that are not of the "4 sets of three + one pair" variety, such as a hand of seven pairs, and a hand consisting of "thirteen orphans" (one each of every "1" and "9" tile, plus one of each non-suited tile, and one more tile of any of these; this hand is one of the yakuman hands).
If all tiles outside of the dead wall have been drawn and no one has completed a winning hand, it is considered an "exhaustive draw". If this happens, players who are at tenpai collectively take 3,000 points from players that are not at tenpai.
Sequences do not loop around, so 8-9-1 and 9-1-2 are not valid sequences. As such, the "1" and "9" tiles, referred to as "terminals", can potentially give you higher-value hands. (Note, though, that if the dora indicator is a "9", the dora is the "1" tile of the same suit.)
If you're curious as to what the non-numbered tiles are: There are four types of tiles with the kanji for "east", "south", "west", and "north". Note that if the dora indicator reveals one of these tiles, the next one in the above sequence (looping back to "east") is the dora tile. However, the tiles themselves cannot make a sequence, and any set including them must be of three or four of the same tile. These tiles can be worth han and count as yaku, if the direction shown matches your position or the current round type (East or South).
Likewise, you will also see tiles that are completely blank, tiles with a green-colored kanji, and tiles with a red-colored kanji. These tiles also form a group for dora indicator purposes, but cannot form a sequence. You must make a set of them out of three of the same tile, but doing so does count as a yaku and adds a han.
Collectively, the non-numbered tiles are referred to as "honors".
Finally, a note on overall scoring. In individual matches, everyone starts off at 25,000 points, with 30,000 points considered the "break even" point. At the end of a game, the score of players in second, third, and fourth, is equal to how many thousands of points they are above 30,000 (with a negative score if their score is below 30,000), rounded to the nearest thousand. The first place player's score, then, is the sum of the other three players' scores (which will be negative), except positive. (If at the end of a game, no one is above 30,000 points, the game moves on to another round.)
And it is with that note that I conclude this crash course on mahjong, and invite those of you who are interested to check out Saki (streaming on Crunchyroll), the story of a girl who has always played mahjong to end up with a score of +/- 0…
(For more information, this page has a list of all the different yaku and their hand values, while this page goes into mahjong scoring in more detail. And this page goes even further into the rules of mahjong.)