Naki strategy
Calling tiles is optional. During a game, players must constantly decides whether to call tiles or not - this decision warrants at least a little observation and evaluation. This page only considers pon and chii, not kan. For strategy regarding kan, see kan strategy.
Assessing calls
Like any decision in the game, opening the hand has advantages and disadvantages.
Advantages
- Allows the hand to complete faster. Sequences can be completed with twice the number of tiles (self draws, and the left opponent's discards). Triplets can be completed with four times the number of tiles (your draws, anyone else's discards).
- Can be used to confirm a yaku. Yakuhai, for instance, are hard to complete without calling pon.
- Can be used to complete a hand you otherwise wouldn't have completed at all. If a hand has 12-man, and the last 3-man is discarded, the sequence will be impossible to complete without a call.
- It is hard for opponents to know whether an open hand is complete or not.
- Disrupts an opponent's ippatsu and affects who gets the haitei draw.
- On the first turn, calls can disrupt chiihou, double riichi, and the option to call kyuushu kyuuhai.
- Can also disrupt an opponent's nagashi mangan.
Disadvantages
- Opening the hand prevents certain yaku, most importantly riichi.
- Lowers the value of other yaku, such as sanshoku and ittsu.
- The hand must have at least one yaku in order to win; it cannot rely on riichi to gain a yaku.
- Reduces the amount of tiles available to discard, making it harder to defend.
- Reveals the called tiles to your opponents, possibly allowing them to deduce the value/contents/yaku of that hand.
Yaku
In order for a hand to win, it must have at least one yaku. Closed hands can always call riichi, but open hands need something else. Tanyao and yakuhai are the easiest/most common of the open yaku; in tenhou.net's houou room, over 90% of all open hands contain one or the other. Other common candidates (from most frequent to least) include: honitsu, toitoi, sanshoku doujun, chanta, and ittsu.
A hand with an unconfirmed yaku may end up in atozuke, a state where the hand only has yaku when it wins off a certain tile. For example, a tanyao-only hand with a "78" wait can only win with a 6, since 9 ruins tanyao. This can lead to furiten if the wrong winning tile is drawn.
Value
Once a hand reaches 4 han, every han afterwards is reduced in value. So if a hand has 4+ guaranteed han after opening, it's often best to call. At this point, the extra speed from calling is often worth the drop from value.
Also consider calling with 2 dora, since the value of a 3 han hand is still good, and it is often not difficult to get another dora.
Lack of value
When a hand is cheap, the opposite effect can occur. If a hand would be cheap when closed, but still have a yaku while open, then calling may be the best choice.
This most often happens with yakuhai pairs. Keeping the pair ruins tanyao and pinfu, often resulting in a riichi-only hand, while a yakuhai pon gives 1 han. There isn't much difference between 1 han closed (riichi-only) and 1 han open. Even when considering the score bonuses from riichi (ippatsu, uradora, menzen tsumo), an open hand's increased speed is often better than the chance for extra points.
Point standings
As with most things in riichi mahjong, the game's specific point standings will alter the need to call. If 12k points are needed to escape 4th in all last, it is best to stay closed even with a 4 guaranteed han hand. If you need 1k points in all last, call as soon as a yaku is available.
Usually call to enter tenpai
Assuming the call would not cause too big of a loss in value (8000 -> 2000 is too big, 12000 -> 4000 is too big), it's often best to call if it would progress the hand into tenpai.
If we have at least 4 han after the call, then no loss would be "too big"; even a yakuman -> mangan is acceptable.
If it is very early in the round, turn <= 5 or so, it may be viable to fish for value, especially if the hand is easy to complete closed.
Prefer calling to complete bad shapes
When the hand is currently closed, prefer to call to complete bad shapes (penchans, kanchans, pairs) before good ones. This is because good shapes are easy to complete by drawing, while a bad shape can act as a chokepoint.
Once the hand is open, it is usually ok to call both good and bad shapes, since the hand has already opened.
Tenpai settlements
After all tiles in the live wall have been drawn, players in noten pay those in tenpai. In addition, depending on the rules, dealers get to keep their seat if they are in tenpai. Therefore, players near the end of the game may wish to call tiles to reach tenpai.
Even if a hand would have no yaku, or would be otherwise impossible to complete, players can still call tiles in order to reach keishiki tenpai ("shaped tenpai"). For the purposes of tenpai settlements, a hand in keishiki tenpai still counts like any other tenpai.