Defense in Depth – Part One
In this series we’ll present a number of advanced tips and tricks for defending, for when simple suji and kabe aren’t enough. Today’s material is taken from chapter four of Hirasawa Genki’s 絶対にラスを引かない麻雀 (Zettai ni Rasu wo Hikanai Maajan).
When you have no safe tiles
It’s far from uncommon to be caught in a situation when you don’t have any safe tiles at all. What do you do at times like that? Let’s start with a quiz question, taken from the NPM’s pro test. The dealer has declared riichi. What would you discard in this situation, and why?
Dealer’s discard pond:
Your hand:
Whether you intend on pushing or folding, the only candidates here are or . It’s just a simple matter of which tile is safer.
To answer this question, let’s consider what makes up the mechanism of tile safety. What makes honor tiles safer than number tiles?
Count the possible waiting shapes!
In order for someone to win off a tile, they must have a related shape waiting on that tile. For example, if 
were to deal in, the other player must have a ryanmen, shanpon or tanki wait. Disregarding kokushi musou, that makes for three different possible waiting shapes. In comparison, if were to deal in the only possible waiting shapes are shanpon or tanki, again ignoring kokushi musou. The extra possibility of a ryanmen wait is what makes more dangerous.
Let’s return to the problem at hand. Compare the possible waiting shapes for and . Ryanmen is eliminated in both cases, and both tiles have equal chances of shanpon, kanchan or tanki waits. However, has the extra possibility of a penchan wait, while does not. is therefore the correct choice.
Here’s another example problem. Which tile is the safest to discard?
Dealer’s discard pond:
Your hand:
You may be tempted to discard the suji . However, let’s try comparing to . Given that they declared riichi discarding 
, we’ll ignore tanki and kokushi musou.
Possible waiting shapes for :
- Kanchan:
x 4 tiles remaining x x 3 tiles remaining = 12 chances - Penchan: x 2 tiles remaining x x 4 tiles remaining = 8 chances
- Shanpon: x 3 tiles remaining x 2 = 3C2 = 3 chances
- Total: 23 chances for a wait
Possible waiting shapes for :
- Ryanmen: x 4 tiles remaining x x 3 tiles remaining = 12 chances
- Shanpon: x 2 tiles remaining x 2 = 2C2 = 1 chance
- Total: 13 chances for a wait
QED is the safer choice. As a bonus, since you have a pair, you can last one extra turn! This is also an important tactic to remember – when you have no safe tiles, discard a tile that you have two or more of. Not only are shanpon and tanki waits less likely, but the initial risk of discarding a dangerous tile is offset by the multiple turns of safety that it buys you.
Any mental shortcuts to do this math?
Also, what is the justification of assuming tanki is unlikely when the riichi indicator is an honor tile?
The simplest rule of thumb is that the more tiles you can see in an area, the safer that area is. Of course, during betaori you should be more careful than that.
When someone chooses a tanki wait, honor tiles are preferable because other players will expect them to be safer, so when someone discards a lot of honor tiles or declares riichi with one, it’s an indicator that they probably don’t have a tanki.
But if Ryanmen waits are more likely to happen then the different wouldn’t be so much, i don’t know where i read/heard that 50% (or it was 70% mmm now i doubt) of the time people win with a ryanmen wait.
Ryanmen are more common because it’s more efficient for people to try to make them. However, early riichis have a higher likelihood of having a weaker waiting shape because people haven’t had time to create stronger waits.
If someone discards weak shapes like penchan or kanchan before they declare riichi, it’s a sign that they had stronger shapes to keep and are more likely to have a ryanmen wait or better. In that case, suji usually become more effective.