Kuikae

Kuikae 「喰い替え」 is a particular restriction applied to tile calls, especially involving chii. It is commonly referred to as "swap calling". Generally speaking, when swap calling is forbidden, when a player calls another player's discard, the following discard cannot be another copy of the tile they just called, nor can it be another tile that also completes the chii that the player just called for.

Examples

Example 1: Different end tile of a chii

1. Player has in hand:
2. Left player discards:
3. Chii is called to form
4. is left over, but cannot be discarded on the same turn, because it completed the on the other end.

Example 2: Middle tile of a chii

1. Player has in hand:
2. Left player discards:
3. Chii is called to form
4. is left over, but cannot be discarded on the same turn, because it is another copy of the tile that was just called.

Example 3: Same end tile of a chii

1. Player has in hand:
2. Left player discards
3. Chii is called to form
4. is left over, but cannot be discarded on the same turn, because it is another copy of the tile that was just called.

Example 4: Pon

1. 
2. Any player discards:
3. Pon is called to form (orientation depending on tile source)
4. is left over, but cannot be discarded on the same turn, because it is another copy of the tile that was just called.

Reasoning

The main purpose of tile calls is to push hands forward and reduce the number of shanten. However, kuikae doesn't reduce the number of shanten, as the tile to discard can make a group with the tiles used for calling to form a mentsu. This kind of behaviour is usually not recognized to be "meaningful" to the player himself/herself, but as a way to "disturb" other players, e.g. utilizing kuikae on purpose to eliminate ippatsu or haitei. More and more people agree with it and then the kuikae rule becomes popular today.

Note that kuikae is not always meaningless to the player himself/herself. The use of kuikae often includes:

1. Skipping a chance to draw to prevent drawing a dangerous tile near the end of a round, especially when in tenpai, due to the noten penalty.
2. Changing the end of a shuntsu (as shown in Example 1) to obtain yaku, especially tanyao, sanshoku, chanta, ittsu, etc.

Some rulesets only forbid discarding the called tile, but allow discarding the other end tile of a chii (e.g. JPML A), therefore it sometimes can be a useful strategy.

External links

• 喰い替え

Kuikae in Japanese Wikipedia

• Why to use Kuikae rule in Riichi Mahjong?