A Quick Look at Mahjong around the World: Mahjong Competition Rules

China is the origin of the oldest styles of mahjong that exist, and also of the most recent notable variation. Mahjong Competition Rules, also known as Chinese Official or as Guobiao Mahjong was created by the Chinese government in 1998 in order to foster a more healthy and safe public perspective towards mahjong.

This game is notable for having one of the largest yaku count in all styles (with a total of 81 different yaku), as well as for having all official rules overseen by the China State Sports Commission (to clearly distinguish 'official' rules from 'house' rules, which almost no other mahjong style can do). Unfortunately, some of its rules are overly complicated and are still debated between official referees and between players, meaning that it inevitably requires casual players to come to agreements over particular rulings.

• There are no dealer keeps in MCR. The game always lasts exactly 16 hands.
• After the end of the south round but before the beginning of the west round, the seats are randomly changed.
• No dead wall is used. A draw only occurs when the live wall runs out of tiles without any players declaring a win.
• When a concealed gong is made, all four tiles are placed face-down with your open melds. They are not revealed until the end of the hand.
• Discarded tiles are placed in ordered rows of six in front of each player, identically to Japanese Riichi mahjong's ponds. Despite there being no furiten rule, you are still required to rotate your claimed tiles in a manner identical to that of Japanese Riichi mahjong.
• A Seven Pairs hand does not need to be made of seven distinct pairs. As long as you have not declared a concealed gong, you may treat four identical tiles as two separate pairs.
• You do not need to reveal bonus tiles right away when you draw them. You may keep them in your hand to reveal at a later point, or discard them for a guaranteed safe turn (discarded bonus tiles may never be claimed by other players).
• You may reveal a bonus tile or create a gong when there are no more tiles left in the wall. If you do so, the game ends in an exhaustive draw (but if you created a promoted gong, other players have a chance to rob the gong before the draw occurs).
• No bonus exists for a Gift of Heaven, Gift of Earth, or Gift of Man.
• Certain yaku can allow you to create 'knitted chows'. These involve having three consecutive tiles in three separate suits (such as a 1-bamboo, 2-dots, 3-characters). More specifically, hands that require knitted tiles require melds of 1-4-7 in one suit, 2-5-8 in a second suit, and 3-6-9 in the third suit.
• Knitted chows are always scored as chows for the sake of making yaku, but are only permissible in hands that score the yaku Knitted Straight, Lesser Knitted Honors, or Greater Knitted Honors.
• An open knitted chow is never permitted. You must self-pick all of the tiles to make the knitted chow, unless the tile needed to make the knitted chow is used to declare a win (Just like with the Thirteen Orphans hand, you are always permitted to win off of a discarded tile to make irregular hands).
• As this is an official government sanctioned sport, the official rulebook includes formalities such as an obligation to bow to your opponents before starting the first hand, or a rule forbidding the naming of a tile as it is discarded. None of these rules are binding in casual games, of course.
• To quote from the English translation of the official rulebook, "There should be a sign on the east wall, bearing the Chinese character "East"; on another wall, a sign bearing the Chinese character "Quiet" to remind everybody to keep the noise down; and on another wall, a sign bearing the Chinese character "Pin" to show to encouragement of moral merit." To my knowledge, very few casual MCR games include these signs.
• Additionally, severe rule breaking is (according to the rules) to be followed by "severe criticism". I would assume many casual games follow this particular rule.
• A player's hand must score at least 8 points in order to declare a win.
• If you self-pick your win, all other players pay you the value of your hand, plus 8 additional points as a bonus for winning.
• If you win off of a discarded tile, the player who discarded it pays you the value of your hand, plus 8 additional points as a bonus for winning. The other two players pay you simply 8 points.
• There are five notable principles for scoring your hand in MCR.
• The Non-Repeat Principle: If a single yaku inevitably implies a less valuable yaku (For example, a Seven Pairs hand will always be a Concealed Hand), only the more valuable yaku is scored: The implicit ones are ignored.
• The Non-Separation Principle: Essentially, you must decide on one particular layout for your hand. You could not treat a 1-1-1-2-2-2-3-3-3 dots as both three pungs and three chows for the purposes of scoring: You must choose one or the other.
• The Non-Identical Principle: Once a meld has been used with one other meld to create a yaku, it cannot be used with a second different meld to score the same yaku again (For example, if you have 1-2-3 dots, 1-2-3 dots, 4-5-6 dots, and 7-8-9 dots, you can only score Large Straight once. You cannot use both of your 1-2-3 dots to score two separate Large Straights).
• The Freedom of Choice Principle: If you can use a meld to score one of two (or more) separate yaku, you're free to choose to score the more valuable yaku.
• The Account-Once Principle: This principle is by far the most complicated. Once you have chosen the first yaku you wish to score that uses two or three melds (after scoring any yaku that relate to four melds, or the hand as a whole, such as All Pungs or Full Flush), any melds not used to score that yaku can only be used once for scoring other yaku. Here's an example to clarify this very confusing rule:
• Your hand has a 1-2-3 dots, 4-5-6 bamboo, and 7-8-9 characters that you use to make a Large Mixed Straight yaku. If your remaining meld is a 7-8-9 bamboo, you can either make a Small Straight (with the 4-5-6 bamboo) or a Two Colors, One Chow (with the 7-8-9 characters), but you are not permitted to make both.
• Additionally, the Account-Once Principle only relates to the elements of your melds, not whether or not they are concealed. Any yaku exclusively based on concealed melds (such as Concealed Gong or Two Concealed Pungs) ignore the Account-Once Principle.
• If a player tries to declare a win with a hand that does not score at least 8 points, he instead must pay each other player 10 points, and may not declare a win for the remainder of the hand.
• If a player tries to declare a win with a hand that does not meet the requirements for a winning hand (four melds and a pair, seven pairs, Thirteen Orphans, or knitted honors), he instead must pay each other player 20 points, and may not declare a win for the remainder of the hand.
• Unlike most other rulesets in which doing so is considered bad etiquette, if you win off of another player's discarded tile, you are obligated to take that tile out of her pond and add it to your hand before scoring. Failure to do so is treated as a false declaration of win (and therefore subject to paying 20 points to each other player).

A full example of scoring, organized in the order of the yaku's value to help determine uses of the Non-Repeat Principle, can be seen here. Another full example of scoring, organized in categories similarly to all other scoring systems on this blog to help players determine what yaku their hands score, can be seen here.