Robbing a Kan

What is Robbing a Kan in Japanese Mahjong?

Robbing a Kan is a one-han yaku in Japanese Riichi Mahjong. This yaku occurs under a very specific condition, making it one of the more dramatic ways to win a hand. Robbing a Kan is a thrilling one-han yaku triggered when you declare ron on an opponent’s attempt to upgrade an open pung into a kong. Though it occurs infrequently, it can catch opponents off-guard and abruptly end a round in your favor. Understanding when to go for Robbing a Kan how to avoid giving opponents this chance—adds depth and excitement to Japanese Riichi Mahjong.

How to Achieve Robbing a Kan？

Robbing an Upgraded Kong: Robbing a Kan happens when another player upgrades an existing open pung (three-of-a-kind) into a kong by adding the fourth identical tile. You declare ron on that very tile, effectively “robbing” the other player’s attempt to complete the kong.

Why Only Upgraded Kong？

If a player declares a concealed kong from their hand, there is no tile to “steal,” since it is entirely internal to their hand and not discarded.

• If a player declares a new open kong off a discard, you cannot rob it either, because that tile is taken directly from the discard, not from an upgrade of an existing pung.
• Therefore, Robbing a Kan uniquely applies to the scenario of upgrading an already-open pung into a kong.

Value: Robbing a Kan is worth one han by itself, regardless of whether your hand is open or closed. It can be combined with other yaku as long as their requirements are still met.

What is the Strategy and Risk of Robbing a Kan?

Timing: The critical moment is when an opponent declares Upgraded Kong. Before they actually complete the kong, you must announce ron if that tile completes your hand. You effectively prevent their kong from forming, using their would-be fourth tile as your winning tile.

Open vs. Closed Hand: Robbing a Kan does not require your hand to be concealed, so both open and closed hands can claim this yaku. If you also wish to claim yaku that require a closed hand (e.g., Riichi), you must already be in that state. Declaring ron via Robbing a Kan itself does not affect those requirements.

One-Han Addition: Like other one-han yaku, you add Robbing a Kan on top of other yaku in your final hand. This can lead to sudden point increases, often catching your opponent by surprise.

Surprise Factor: Robbing a Kan is relatively rare, but it can drastically change the flow of the game. Opponents sometimes forget about the possibility when greedily upgrading their pung into a kong.

Risk of Declaring Upgraded Kong: Players typically declare Upgraded Kong to gain extra dora flips and a supplementary draw. However, if they suspect someone might be waiting on that very tile, they risk a Robbing a Kan loss. Skilled players weigh the risk–reward of revealing more of their hand versus the chance of giving an opponent a winning tile.

Defensive Awareness: Even if you have the tile to upgrade to Upgraded Kong, consider the discard pool and your opponents’ visible waits. If someone has shown signs of waiting for that tile, you might hold off on the upgrade.

Combining with Other Yaku: A Robbing a Kan win can combine with other yaku in your hand. For example, if your hand also qualifies for All Simples or Half Flush, you get one additional han from Robbing a Kan, boosting your total score.