Riichi Rules and Implications

14.1 Declaring Riichi

Riichi (立直/リーチ) is the defining mechanic of Japanese mahjong. When your hand is closed (no open melds) and you reach tenpai, you may declare riichi by stating "riichi," placing a 1,000-point deposit on the table, and turning your next discard sideways to mark the declaration. After declaring, your hand is locked—you cannot change it (with the sole exception of calling a closed kan if it does not change your waits). You must win on whatever wait you have, or reach the end of the hand still in riichi.

14.2 Benefits of Riichi

Yaku: Riichi itself is a 1-han yaku. This is often the easiest yaku to achieve—any closed tenpai hand qualifies, regardless of composition.

Ippatsu (一発): If you win within one full turn cycle after declaring riichi (before anyone makes a call or your turn comes back), you receive 1 additional han. This bonus cannot be aimed for but adds significant expected value to riichi hands.

Ura dora (裏ドラ): When you win after riichi, tiles beneath the dora indicators are revealed as additional dora indicators. Each matching tile in your hand adds 1 han. Ura dora provide approximately 0.5-0.7 expected extra han on average.

Intimidation: A riichi declaration announces to all opponents that you are tenpai and attacking. This forces opponents into defensive mode, potentially preventing them from completing their own hands.

14.3 Costs and Risks of Riichi

1,000-point deposit: If you don't win, you lose 1,000 points (the deposit goes to the next winner). In a close match, this can matter.

Hand is locked: You cannot adapt to changing game conditions. If an opponent also declares riichi or if dangerous tiles accumulate, you are stuck pushing forward.

Information leak: Opponents know you are tenpai and will play defensively. Against strong opponents, this can reduce your win rate significantly.

Furiten risk: If your winning tile passes and you cannot or do not claim it, you enter permanent furiten (tsumo only). With a locked hand, this is devastating.

14.4 When to Declare Riichi

The general heuristic, well-supported by Japanese mahjong analytics, is: riichi is correct in most situations when you have a closed tenpai hand. The combination of the riichi yaku, ippatsu chance, and ura dora expectation makes riichi's expected value positive in the majority of cases. However, there are important exceptions:

Consider dama (not declaring) when: (1) Your hand already has high value without riichi (e.g., mangan+ with existing yaku and dora). (2) You have a bad wait (low ukeire like tanki on a common tile). (3) Game situation favors defense flexibility (you are in first place and don't want to lock yourself into attacking). (4) Your hand qualifies for valuable yaku that riichi would not improve (e.g., already at 4+ han, where riichi adds less marginal value). (5) You want to be able to switch to defense if an opponent declares riichi.

Riichi is especially strong when: (1) You have a good wait (ryanmen on tiles with many copies remaining). (2) Your hand has few han without riichi—riichi + ippatsu + ura dora has the highest marginal value on low-han hands. (3) You are not in first place and need points. (4) Early in the hand when the wall still has many tiles.

14.5 Riichi Strategy Considerations

Timing: Early riichi (turns 6-10) is generally stronger than late riichi (turns 14+) because more tiles remain in the wall, giving you more draw opportunities. Late riichi on a bad wait may simply donate 1,000 points.

Wait quality: A ryanmen riichi with 6+ acceptance tiles is much stronger than a tanki riichi with 2 acceptance tiles. Wait quality should influence the decision significantly.

Score context: In the last round, a player in 4th place should riichi aggressively (needing points), while a player in 1st might stay dama to maintain defensive flexibility.

14.6 Riichi Frequency Data and the "Riichi Judgment" Debate

One of the most actively debated topics in Japanese mahjong strategy is how often to declare riichi. Data from Tenhou's highest-level tables (鳳凰卓, Houou-taku) shows that strong players declare riichi on approximately 18-22% of all hands they play. The riichi win rate (percentage of riichi declarations that result in a win) among these players is approximately 45-50%.

The "digital mahjong" (デジタル麻雀) school, exemplified by Totsugeki Touhoku's (とつげき東北) statistical approach, generally advocates for higher riichi frequency — arguing that the expected value of riichi (factoring in yaku, ippatsu, ura dora, and intimidation) is positive in the vast majority of closed tenpai situations. The main exceptions, as documented in the statistical analyses, are: (1) hands already at mangan+ value without riichi, (2) bad waits (tanki on a tile with 1-2 remaining copies) late in the hand, (3) situations where defensive flexibility is critical (leading in all-last), and (4) hands where dama allows wait improvement on the next draw.

Sasaki Kotarou (佐々木寿人), a prominent M-League professional known for aggressive riichi play, has stated in interviews that his personal riichi rate is among the highest in professional play, and that he considers under-riichi-ing to be a more common error than over-riichi-ing among intermediate players. This view is shared by many analytically-oriented professionals, though more traditionally-minded players advocate for greater selectivity.