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Furiten and Defense

Why can't you ron when you are in tenpai? And when someone declares riichi, how do you pick safer tiles?

Furiten: you cannot ron on your own discards

If any of your winning tiles is in your own discard pond, you cannot win by ron. This is called furiten. You can still win by tsumo.

The key word is "any": if even one of your waits is in your pond, the whole hand is furiten. The game shows "Furiten" above your hand to remind you.

Two more kinds of furiten

• Temporary furiten: someone discards one of your waits and you do not win (you press Skip). Until your next discard you cannot ron on anyone's tile.
• Riichi furiten: after declaring riichi, if you let a winning tile pass even once, you cannot ron for the rest of the hand; only tsumo.

So before you riichi, check whether one of your waits is already in your pond. Choosing a different wait often avoids furiten.

Why defense matters

When you deal in, you alone pay the whole score. When an opponent declares riichi or is clearly building a big hand, not dealing in is often worth more than winning a small hand yourself.

Giving up on winning and only discarding safe tiles is called folding. A simple rule: if you are far from tenpai (2 shanten or more) and an opponent has declared riichi, consider folding.

Safe tiles: genbutsu

Genbutsu are tiles the riichi player has already discarded. Because of furiten, the riichi player cannot ron on them.

• After the riichi, any tile someone else discards and the riichi player does not win on stays safe from then on (riichi furiten).
• When someone declares riichi, looking for genbutsu is the first step of defense.

Safer tiles: suji, kabe and honors

With no genbutsu left, use these clues:

• Suji: if the opponent discarded a 4, then 1 and 7 cannot be a two-sided wait (both 1-4 and 4-7 waits need the 4). Likewise 5 covers 2 and 8, and 6 covers 3 and 9. Suji only protect against two-sided waits, not closed, pair or double-pair waits.
• Kabe (walls): if all four copies of a tile are visible (say all four 7 circles), nobody can use 7 in a run, so 8 and 9 circles are relatively safe.
• Honors: an honor tile with 2 or 3 copies already visible can only be won on with a pair wait, so it is fairly safe.

The Hard AI judges danger with exactly these methods.

When to push

You do not have to fold every time. Consider attacking when:

• you are already in tenpai with a good two-sided wait;
• your hand is big (mangan or more) and worth the risk;
• the match is nearly over and you need this hand to catch up.

On Easy the opponents never fold; switch to Normal or Hard and you will feel the difference defense makes.

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