Kuikae

Kuikae 「喰い替え」, commonly referred as "swap calling", is a rule on discards after making a tile call.

If kuikae is disabled ("kuikae nashi"):

• When a player calls another player's discard, the following discard cannot be another copy of the just-called tile.
• When a player calls chii, the following discard cannot complete the just-called chii.

Kuikae nashi is the more common rule used today.

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, a kuikae call doesn't reduce the number of shanten, because the discarded tile would've completed the mentsu.

When kuikae is allowed, players can:

• Call tiles in order to easily disrupt others. Players can make "meaningless" calls in order to interrupt other players' ippatsu or the haitei draw.
  • Calls can also be used to skip having to draw a (potentially dangerous) tile late in the round. This can be especially important if in tenpai, due to the noten penalty.
• Call tiles in order to easily raise the value of their hand. Kuikae can be used to change the end of a sequence (as shown in Example 1) to obtain yaku, such as tanyao or sanshoku. It can also be used to obtain dora, such as calling a red five, then discarding a five afterwards.

By restricting kuikae, both cases become less prevalent: it is harder to disrupt players for the sake of disruption, and it is harder to gain value with an otherwise useless call. Allowing kuikae is not an inherently bad thing - these "disruptive" tactics have a strategy of their own. However, since more players prefer to play with kuikae restricted, rulesets often include the kuikae rule.

Even in a kuikae nashi ruleset, it is possible to call tiles to disrupt others or gain value. As mentioned, though, it becomes harder to do so.

Circumventing Kuikae

With certain complex tile shapes, it is possible to make kuikae-like tile calls without violating the kuikae rule. For example:

1. Player has in hand:
2. Left player discards
3. Chii is called to form
4. are left over.
   1. cannot be discarded on the same turn due to kuikae; however,
   2. is not connected to , and can be discarded immediately.

If was the only yaochuuhai in the hand, the hand now acquires tanyao. This would not have been possible if the player called chii with to form , in which case discarding would be forbidden by kuikae.

Rule Variations

Main article: Rule_variations#Kuikae

Many, if not most, rulesets disallow kuikae. There are a few variations to the rule, though:

• Generally, when kuikae is not allowed, you are unable to discard the exact tile drawn, and when calling chii, are unable to discard any tile that would complete said chii.
• Some rulesets (such as JPML A) may disallow discarding the exact tile that was called, but allow any other discard. For example, under this rule, with a sequence of 123, you can call chii on 4, discard 1, and have a 234 set.

External links

• 喰い替え

Kuikae in Japanese Wikipedia

• Why to use Kuikae rule in Riichi Mahjong?