Riichi 「立直」 (reach or ready) occurs when a player with a concealed hand is one tile away from winning, declares "riichi'' and places a 1000 point bet on the table and rotating his discarded tile 90 degrees. If the discarded tile was claimed for mahjong the riichi declaration does not count. If the discarded tile is claimed for a chow, pung, or kong the player rotates his next discarded tile. Declaring riichi is worth one yaku.
A player is not allowed to declare riichi if there are less than four tiles in the wall.
After riichi is declared the player is not allowed to change his hand or claim (chow, pung, or kong) any additional tiles. A concealed kong is allowable if the tile is drawn that matches up with a concealed pung and as long as this does not change the original waiting pattern. Note: In some varaiations concealed kongs are not allowed after a riichi declaration.
A player who is furiten may declare riichi but can only win on a self-drawn tile that was previously discarded.
A player who, after declaring riichi, chooses not to win on a discard that completes his hand, becomes furiten for the remainder of the round and may only win on a self-draw (unlike the state of being temporarily furiten if a player chooses not to win on a discard when they have not declared riichi).
A player who wins after declaring riichi gets to reveal any tiles underneath the dora indicators (mekuri-pai) or kan dora indicators.
The riichi bet is given to the player who wins the hand. In case of a draw it remains on the table and is claimed by the next winner.
If all four players declare riichi and a win is not declared after the fourth player's discard the hand ends in a draw. Each player must reveal their hand afterward.
One shot
One Shot (iipatsu 「一発」) is winning, on either a discard or self-drawn tile, within the first uninterrupted go-around after declaring riichi.
Double Riichi
Double Riichi (daburu riichi 「ダブルリーチ」) is when a player declares riichi within the first go-around, or turn. In order for a player to qualify for double riichi, the go-around cannot be interrupted by a chow, pung, or (concealed or melded) kongs before the riichi declaration.
Open Riichi
Open Riichi (oopun riichi) is when a player declares riichi and "opens" or reveals the section of his hand that he is waiting to complete. Declaring open riich is worth 2 yaku if a player who declared riichi deals the winning tile, or upon a self-drawn win, and worth a yakuman if a non-riichi player deals the winning tile. It is an uncommon yaku moreso used in house rules and social games rather than in tournaments. The value and the way the hand is revealed may differ as illustrated in Akagi1, where the entire hand is revealed and a player is not penalized a yakuman for dealing into it.
Value
- Riichi: 1 han
- Iipatsu: 1 han
- Daburu Riichi: 1 han
- Opun Riichi: 2 han/Yakuman