Riichi strategy
For strategy regarding riichi mahjong itself, see Strategy
Calling riichi comes with various considerations. While declaring riichi does allow for higher scoring hands, players must not be blinded by the opportunity without considering the risks. It may be a good idea, or it may do nothing but harm you. Regardless, it's best not to blindly call riichi every time you reach tenpai.
Assessing riichi
When it comes to riichi, one must weigh the advantages and disadvantages.
Advantages
- Riichi is a yaku. It grants 1 additional han and allows any closed hand to meet the yaku requirement.
- You can score additional han through ippatsu and/or ura dora. In addition, you are more likely to tsumo with a riichi, increasing the chance for menzen tsumo. When considering these bonuses, a riichi is worth an average of around 1.5 han.
- Each kan formed by any player provides a kan uradora to the riichi, in addition to the regular kan dora.
- Other players may defend against a riichi call, giving up their hands to avoid dealing in.
Disadvantages
- By rule, the hand is locked. Therefore, it is impossible to change the composition of the hand in order to get a better wait or an improved score.
- A riichi hand can no longer defend. If other players manage to reach tenpai, you could deal in.
- Riichi usually lowers the hand's win rate. A defending player is less likely to deal in, so you'll be less likely to win.
- If you do not declare a win on the first possible winning tile, you will enter furiten.
- A "riichi stick" of 1,000 points is spent to call the riichi, with the hopes of winning it back. However, other players may win the hand and capture those 1,000 points instead.
Considerations for riichi
Once again, riichi is a discretionary play. Every time you call riichi, some risk is involved, so you should consider various factors before making the call. At the same time, riichi is strong, so there are many cases where you should use it. Whenever you should or shouldn't riichi depends on the gamestate.
As an alternative, you can go damaten, which is simply a closed tenpai that hasn't called riichi. Another alternative is to give up the hand entirely.
Speed
There is an advantage to being the first to tenpai, and thus an advantage to being the first to declare riichi. Only one hand can win per round, so faster hands can win before anyone else. While a non-tenpai hand is limited to chii and pon, a tenpai hand can ron from any player. The earlier riichi is declared, the harder it is for opponents to defend or attack against it.
If you are first to tenpai, it becomes difficult for your opponents to attack, since going from iishanten to tenpai can take a while (even with great tile acceptance).
- If an iishanten opponent decides to attack, they will often have to spend multiple turns to achieve tenpai. This means they may need to discard dangerous tiles for multiple turns, which could be tiles you could win with. You could also tsumo before then, or win after they reach tenpai. Of course, the exact speed depends on luck; a player could reach tenpai just after you declare riichi.
- If an opponent at iishanten decides to fold, you will have one less player to worry about.
Due to these advantages, a player who declares riichi first will often exert pressure on the other players. This, in turn, can make other players give up their hands. Of course, this is not guaranteed, especially if the point standings force some other players to take on offense at all costs. However, you will still have the advantages listed above.
Conversely, a chasing riichi (riichi after another player has declared riichi) is weaker for the same reasons.
Hand shape and waits
Once a hand reaches tenpai, the chance of winning largely depends on the tile waits. Hands waiting on three or more tiles, such as ryanmenten or sanmentan, have a favorable chance of winning, while one tile waits like kanchan or tanki are less likely to win.
Since most of the risks of riichi only apply if the hand fails to win, having a good wait means that riichi is more desirable. Bad shape waits may be more pressured to keep the possibility of failure in mind, as well as the possibility of changing the hand into having a better wait.
If you are in furiten, you should be more wary about declaring riichi.
- A furiten two-sided wait is around the level of a non-furiten one-sided wait. It's a bit less likely to win, but the average win score is a bit higher due to guaranteed menzen tsumo.
- A furiten three-sided wait (>=9 tiles left) is relatively strong. Don't be afraid to riichi with it.
Score
Riichi gives 1 han, and possibly more via ippatsu and ura dora. Since every han doubles your score until you reach mangan, these are all valuable; riichi triples your average score. However, there are rare cases where score does not matter.
- When riichi wouldn't actually change your hand value. For example, haneman is scored with 6 or 7 han. If you have a 6 han hand, riichi's +1 han would still result in a haneman. Getting mentsumo, ippatsu, and/or ura dora will increase it up to baiman, but these are unreliable, and the difference between haneman and baiman is too small to be worth the risk.
- When you are in first with a large lead. In this case, you may damaten to increase hand win rate, allowing you to end the game faster.
- When you have a valuable hand. If you have a guaranteed mangan or higher hand without needing riichi, the extra score may not be worth the loss of win rate.
That being said, the extra points from riichi often do matter. Mahjong is a game about scoring the most points, after all.
Winning chance
Pressing players to defend will lower your chance of winning. If a hand has a yaku other than riichi, declaring riichi will generally lower your winrate by about x4/5. Since riichi more-than-doubles your score until reaching mangan (1 han from riichi doubles score, then potential extra han from ippatsu/uradora), when you are below mangan, riichi will generally has a higher expected value.
If you don't care about points, but you do care about winning, you should dama. As mentioned above, if you are in the lead by a large amount, dama.
Hands which have an extremely poor wait (e.g single tile wait on dora) are so bad that riichi doesn't reduce their chance of winning by much.
Point standing
In the first half of the game, your exact point standing (the # of points between you and 1st/2nd/3rd/4th place) is generally not a big concern. There are many opportunities to make up differences : a player who's ahead can hardly afford to rest on their laurels, while players who are behind are not as desperate. Thus, situations tend to be more "general" - riichi's increased reward is usually appreciated, its intimidation effect more often felt, and it is more often a good idea.
When the game is closer to its end (usually in the South round; can be earlier if a player is close to bankrupting), the game's precise point standing matters more. Most places focus heavily on the player's end-of-game placement, so going from 3rd to 2nd is a major jump, and going from 3rd to 4th is a major blow. Even a +1000 point win is valuable if it causes you to rise in placement, or lets you keep your current placement.
- Players that are ahead should be more willing to dama. Late in the game, increasing your point lead doesn't matter as much, but the risk of dealing in matters more. Also, as mentioned above, dama increases your winrate, allowing you to end the game faster.
- Meanwhile, players in 4th by a large amount are often forced to riichi, hoping for a big hand. Players in the middle should analyze their own specific situations to determine if riichi is right. If being in 4th place confers a huge penalty (such as high ranked gameplay in tenhou.net and Majsoul), players not in 4th may want to dama to end the game faster, even if riichi could let them rise a place.
- The 1000 points used to declare riichi could cause you to drop down a rank. If this is the case during all last, you probably shouldn't riichi if you have another yaku.
- If a damaten win and riichi win would cause you to end up in the same placement, and it's all last, you should dama.
Overall: in the earlier end of the game, going for raw points can be a good idea. In the later end, aiming to retain (or improve) your placement usually matters more than the points themselves. This consideration will depend on the game's oka and uma settings.
Hand lock
By declaring riichi, the hand is locked - you cannot upgrade the hand to improve the wait, gain yaku, or play defensive.
Waiting for upgrades
Being the first to riichi is a big advantage of itself. So, if you want to delay riichi to wait for an upgrade, you should have many tiles that you could upgrade off of. As a contrived example:
Waiting for:
You could upgrade the hand to a two-sided or better wait with: 
, which is up to 48 tiles. When considering the number of upgrades, you should consider every visible tile. You must also watch out for furiten.
As the round progresses, you should be more willing to riichi than to wait for an upgrade; you don't have as much time to wait for an upgrade.
Note: when you reach tenpai but are waiting for an upgrade, it's often best to stay at iishanten, unless you have an expensive hand. If you enter tenpai with a 46-pin middle kanchan, you have 8 tiles worth of upgrade. If you decline tenpai, you'll often have more than 8 tiles to upgrade with. For example, if you discard 6-pin, leaving 4-pin and a 2334-man shape, you have 18 tiles worth of non-furiten uprades.
Defense
The hand lock prevents you from defending, which is the biggest risk of declaring riichi. Often, the reward is worthwhile. Even without riichi, it is often best to keep tenpai instead of defending. But if the risk of dealing in is greater than riichi's extra value, then it can be a bigger point of concern.
For example, say it is South 2, you are in 2nd place, 1st place is 14000 points ahead, but 3rd is catching up. You shouldn't riichi with an otherwise pinfu-only hand, since an extra 1000-2900 points will not impact placement, but dealing into another player can cause you to drop down placement. It is possible to overtake the lead, if you ron 1st with a riichi ippatsu + 1 ura dora, but this is not worth the risk.
Furiten
Declaring riichi means that, if the player declines the first possible ron, they enter permanent furiten. Meanwhile, if a damaten hand skips a win, it is only in furiten until the next discard.
First, damaten has better control over yasume. If a riichi hand wins off a bad wait, you have to accept it or enter furiten. However, since riichi adds an average of around 1.5 han, this is only an issue if the waits differ by 3+ han. Even then, you may want to riichi despite this.
Second, a damaten hand can try and target a specific player. You may want to ron to get a player below 0 points, ending the game immediately. Or you may wish to avoid calling ron on a player with 0 points, to not end the game. This can also be done to change placement when near all last (e.g. targeting 1st place as 2nd). However, since riichi gives a hefty point bonus, a riichi hand might improve your placement even if you tsumo or ron the "wrong" player.
Oikake riichi
Oikake riichi 「追いかけリーチ」 is a "chasing riichi", or a declared riichi after another player had already declared riichi. In this state, two or even three players have simultaneously declared riichi. In this state, players are locked into a "riichi duel" - any riichi declarer is liable of playing into another's riichi call.
Players often declare chasing riichi because they have no option to defend, or when they have a big hand. At the same time, if after an opponent riichi's, you reach a good wait tenpai, then trying to win is often better than folding. When you do have the option to defend, the decision to push or fold should depend more on shanten, tile acceptance, and wait rather than the value of the hand.
If abortive draws are enabled, the hand will end in abortive draw when all four players declare riichi (after the 4th riichi declarer discards a tile).
External links
- 【麻雀講座】ダマテンにすべき手の基準～"場況"という曖昧さを解消する (YouTube)
- Unimaru's coverage of riichi vs damaten