Ippatsu

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Ippatsu
Type Yaku
Kanji 一発
English One shot
Value 1 han
Speed Riichi dependent
Difficulty Luck

Ippatsu 「一発」 is a yaku that is completely dependent on riichi. After declaring riichi, if the player wins before their next discard, and before anyone makes a tile call, then ippatsu is awarded. You must declare riichi to score ippatsu, so a hand can never have ippatsu by itself.

While ippatsu is generally considered to be a standard yaku, certain rulesets do not use it, in order to reduce variance and lower the value of a riichii. In general, when sitting down to play a game, ippatsu is counted unless otherwise specified or agreed on before the game.

Development

In order for ippatsu to be counted, the hand must win before the hand in riichi discards its next tile. The earliest possible chance to win with ippatsu comes from the shimocha's discard (player to the right). The latest possible chance to win with ippatsu is with the player's next drawn tile after the riichi declaration.

Furthermore, no interruption to the turn must occur. This means that tile calls will immediately end the chance for ippatsu. This includes any calls for kan except for a robbed kan (chankan). In sanma, the call for kita also denies ippatsu. If the riichi player declares kan or kita, ippatsu is still denied.

To repeat: even if a hand is won before the next discard, if a call is made, ippatsu is denied. Thus, players can purposefully make tile calls in order to disrupt another player's chance for ippatsu.

Examples

Jigoku ippatsu tsumo by Pekora.
Kan is called prior to the riichi call; and the hand wins on the next draw without interruption. Therefore, ippatsu is valid.
This hand wins on a discard before the next draw.

Ippatsu nullified

In this example, the hand wins from an opponent discard before the next tile draw. However, two tile calls were made prior to the win. So, ippatsu is invalid here.

Compatibility

RCH DRI IPP SMO TAN PFU IPK ITT YAK SDJ SDO TOI SNA SNK CHA JUN RPK SSG HRO HON CHN CHI RIN HAI HOU CHK
IPP

Ippatsu is unique as it requires riichi to even be applicable. Thus, it is impossible for a hand to score with ippatsu alone. At the very minimum, a hand could be riichi with ippatsu.

Unlike riichi, ippatsu cannot be combined with two yaku: rinshan kaihou and houtei raoyui. Rinshan requires a kan call, which would invalidate ippatsu. As for houtei, a riichi declaration must be made with at least 4 tiles left in the live wall. That leaves the very last possible tile draw (and discard) belonging to the riichi declarer.

Note that chankan is compatible with ippatsu. When winning off chankan, the kan call is interrupted, so ippatsu is retained.

With haitei

Last chance to call riichi, with possible Ippatsu and haitei.

The last possible chance for riichi comes when there are eighteen tiles left in the walls, counting the fourteen tiles in the dead wall. That leaves four tiles left for regular player draws. After the last possible riichi, if no tiles are called, every player would have exactly one tile draw left. Therefore, the last tile would go to the riichi declarer, allowing both ippatsu and haitei to be scored. Naturally, players may make tile calls to disrupt both yaku.

External links

Ippatsu in Japanese Wikipedia