This is a part of “UmaiKeiki’s defense guide — Betaori and Suji” posted in Osamuko’s Mahjong Blog
All thanks to UmaiKeiki =)
Introduction to defense
Defense in Mahjong is focused primarily on how to avoid dealing into opponents’ hands. In other words, playing defensively means making fewer payments. You know that saying “a penny saved is a penny earned”? This is VERY true in Japanese Mahjong! Your points are valuable; don’t let someone take them without a fight!
As with many gambling games, the good hands will come to you eventually; you must be patient and wait. Until then, it is only natural for some of the other players to reach Tenpai faster than you, and to win before you do. Don’t sweat it! However, why should YOU be the one to deal into their hands? This can hurt your standing to the point where recovery is almost impossible, and it gives the other players a lead over you as well. Essentially, Japanese Mahjong seems to have become a game which is not about “winning more” but about “losing less”. It is considered a wiser move to preserve the points you have rather than to risk them on the chance of getting some more. Therefore, the key to defense is to identify “safe tiles”, which are tiles with a low probability of being an opponent’s winning tile.
Fortunately there are a number of strategies that you can use to find safe tiles and identify which are more or less safe than others. The basics are Betaori, Suji, and Kabe. Against advanced players you may be interested in Damaten and Saki-giri. (I originally intended to include them all in this guide. Maybe there will be a “Part 2″ in the future.)
Finally, a caution about discard reading. While it’s most certainly possible to guess an opponent’s waits and hand tiles, it’s not an exact science. Because of this, it seems to be regarded as some kind of “black magic”. Most people are afraid of it to some extent, so don’t expect every discussion you have about discard reading to be entirely supportive of your ambitions.
Betaori
Betaori is the number one defensive strategy. Most people will use it as soon as someone declares Riichi, as it means that person is most likely to win this round. Don’t worry about other people winning — it happens. What you should be worried about is dealing into that person’s hand and thus being the only one to lose points. To avoid this, you must often discard otherwise useful tiles from your hand and take apart mentsu.
Ouch! Taking apart your hand? Some people hear this much and decide not to bother. I maintain that this is an important strategy and urge you to give it a try. Just watch what happens when someone declares Riichi. Chances are the others are going to start discarding tiles that very clearly indicate that they are in Betaori. So if anyone is going to deal into that Riichi, you’re the most likely! And consider this: that opponent is Tenpai and could win at any second, but if you are still something like 2 Shan Ten, why would you keep attacking? It would take you much longer to catch up, and you would most likely have to discard some dangerous tiles to do so.
By the way, the No Ten payments are no excuse to avoid Betaori. If the round ends, you’ll only be paying 1000, 1500, or 3000 points, and this is usually a lot better than dealing into someone’s hand. (Anything with Riichi, specifically, will usually be worth more than 3000 points. USUALLY.) Besides, you should be able to make back those points in due time. Also, if you are playing “inflated” Mahjong, No Ten payments are really insignificant compared to the average winnings, so don’t worry about it.
OK, so we know that we’ll be breaking down the hand and trying to avoid a loss. How exactly do we do this? Well, the strategy goes like this:
1. Discard Furiten tiles
2. Discard into impossible waits
3. Discard into improbable waits
4. Discard into improbable yaku
5. Break apart An Kous etc…. and cross your fingers.
STEP 1: FURITEN TILES
At any given point in time, there is one 100% safe tile. This is the tile just discarded by your Kami Cha, aka the player to your left. At that moment, all 3 opponents are Furiten for that tile at the same time. So if you have the same tile in your hand, go ahead and discard it now because nobody can Ron it.
On a similar note, if all 3 opponents have discarded the same tile at some point in the game, they are all Furiten for that tile. So if you have the fourth one, it also is a 100% safe tile. The difference here is that this one stays safe; the Kami Cha’s discard is only safe for the current turn. Since some opponents will no longer be Furiten for the Kami Cha discard next turn, discard that one first!
Since you’ll be using Betaori mainly against an opponent who has declared Riichi, you can focus on discarding that person’s Furiten tiles. Just take a look at their discard history: they are Furiten for everything they’ve discarded so far. Also, you can use tiles that others have discarded since the Riichi was declared. Depending on the strictness of your house’s Furiten rule, the others’ discards may be safe for only one turn. However, if the person who declared Riichi didn’t call them the first time, you can reasonably expect them to still be safe. (The only reason they would become dangerous again is that it wasn’t considered advantageous to Ron off that specific opponent, so the person who could have won decided instead to become temporarily Furiten and wait for that tile to come from someone else.)
Now don’t get ahead of yourself! Furiten tiles are the safest tiles you can deal. So if you are facing someone who has declared Riichi, discard their Furiten tiles before anything else. The key here is STALLING. Discarding a Furiten tile buys you one more round; for each round you stall, they could get their winning tile from someone else, meaning that you successfully dodged making the payment! Also, since more Furiten tiles can appear during each round, defending will become easier for each round you stall.
STEP 2: IMPOSSIBLE WAITS
Impossible waits are somewhat rare, but keep an eye on the discards and you might find some. Jihai are common candidates for impossible waits: since they can’t be used in shuntsu, the only possible waits are Shanpon and Tanki. (Kokushi Musou is an exception, but it should be easy to tell whether it is a threat.)
Suppose you have a Chun in your hand, and you can see the other three Chun have been discarded already. That means nobody can have a shanpon or tanki wait on Chun, so it is an impossible wait. This also works if you have 2 Chun and the other 2 are discarded, or if you have 3 and one is the Dora indicator, or really any situation in which all 4 are visible.
Now finding impossible waits on number tiles is a bit harder, since you need to block any possible Shuntsu. Let’s suppose all four of the 
and 
are visible. That means none of your opponents can have a shuntsu containing either 
or 
, so the only waits possible on and are Tanki and Shanpon. So if you have the last or the last , they are 100% safe.
STEP 3: IMPROBABLE WAITS
OK, we know that Furiten and impossible waits give us safe tiles, but what happens when we run out of safe tiles? We have to start discarding “mostly safe” tiles, which means that it is POSSIBLE for an opponent to be waiting on them, but it is not PROBABLE.
Let’s assume your opponents are fairly intelligent. They probably know a lot of attacking strategy. What kind of wait do you think they’ll use? Ryanmen? You bet! Since Ryanmen is considered the “best” wait, you’ll naturally see opponents using it most of the time. The less efficient the wait, the less likely someone is to Riichi on it. So if you are trying to avoid dealing into a Riichi, look for tiles that could only be used in “bad” wait types like Tanki, and work your way up. The goal is to just avoid dealing any tiles that could be used in Ryanmen waits.
The strategy for Tanki and Shanpon waits is pretty much the same as for impossible waits as described above. Let’s go back to the Chun example. Suppose you have one Chun in your hand, and none are visible in discards. Then it’s a “live” tile, and thus very dangerous. Now what if there were one Chun visible in discards? Then the efficiency of a Shanpon wait on Chun is reduced, but someone might still go for it just because they want to get that extra Han. What if 2 were visible? Then Shanpon is impossible; the only wait is Tanki. That makes it a lot safer; the only time you should worry about dealing it is when it’s the Dora.
After we run out of Tanki and Shanpon waits, let’s look for number tiles that could deal into Kanchan and Penchan waits, but still avoid Ryanmen. To do this, we’ll need to “block off” any Ryanmen waits.
Let’s suppose that all four of the are visible. That means there can be no Ryanmen waits on 
and 
. (Note however that someone might be waiting on 
, as it would still count as Ryanmen.) The only possible waits on are Tanki, Shanpon, and Kanchan; the waits on are Tanki, Shanpon, and Penchan. If you have one of those tiles in your hand and at least two are visible on the table, Shanpon is no longer possible. And if 3 were visible and you had the last one, Tanki is impossible and the only possible wait would be Kanchan/Penchan.
We can also use Suji to identify which Ryanmen waits are more dangerous than others. To cite the classic example, suppose your opponent is Furiten for . That means and Ryanmen waits are less probable, since your opponent is already Furiten for one side. In this case, the is safer because the only waits left are Shanpon and Tanki. The could be used in Shanpon, Tanki, Kanchan, and Penchan.
While Ryanmen is the main threat, do be aware that Kanchan and Penchan are somewhat dangerous. Sometimes people will use Kanchan waits as a really sneaky way of getting someone to throw them the Dora. And Penchan might be used in the interest of speed. To see how that works, put yourself in their shoes: suppose you are the first one to reach Tenpai, but you have an “inefficient” wait. You probably won’t declare Riichi just yet, because you are more likely to draw a tile that will upgrade it to a better wait than you are to draw the winning tile. So you’ll hold off until a better wait forms and then you’ll Riichi. The exception would be if your wait were Penchan. Penchan waits are really hard to upgrade; you are more likely to draw the winning tile than you are to upgrade the wait. That means if you decide to upgrade, you’ll be giving the opponents plenty of time to advance their hands and catch up. You’ll probably try to Riichi now while they are weak, because it will force more of them to defend. Because of this, expect Penchan Riichis to be more frequent in early game than in late game.
STEP 4: IMPROBABLE YAKU
When you reach the point where anything you can discard would deal into a dangerous wait, it’s time to choose tiles that ruin the opponent’s chances of getting extra Han. You can still get hit by Ron, but at least the payments will be smaller.
For example, if you think the opponent might be aiming for Tanyao, deal 1′s and 9′s. There is always a chance that the opponent has waiting for or , but if they really did have Tanyao, the payment you make for dealing is less than what you would pay for dealing .
And if you think they might be aiming for Chanta, start by dealing 5′s, then 4′s and 6′s. Again, there is always a chance that the opponent has waiting for or , but if they really did have Chanta, the payment you make for dealing is less than what you would pay for dealing .
If you suspect they might be aiming for Hon Itsu, just discard some tiles from a suit they probably don’t have. Sometimes it won’t be a Hon Itsu, but the majority of tiles will be in one suit. In that case, you can sometimes use their early number tile discards to find out what suits are safe.
Maybe your opponent built a wait around the Dora? Don’t deal any tiles that are close to the Dora! Also, don’t deal any red 5′s until you see the nonred 5 pass.
STEP 5: BREAK APART AN KOUS, ETC.
This is something of a “last resort” strategy. If you have two, three, or maybe even all four instances of a tile in your hand, try discarding one. It’s still dangerous, BUT if it passes, you know the rest are safe! Then you can just discard one each turn until you run out. The more instances of a tile you have, the longer you can stall, meaning some more Furiten tiles or other safe tiles are likely to come out.
Another good move might be to discard tiles such that there are already several instances of that tile visible on the table. Your opponents might not Riichi if they know most of their waiting tiles are accounted for.