The Suji Trap

Mastered simple 1-4-7 suji yet? Good, you'll find defending a bit easier once you start using them. Now why don't we test your newfound suji knowledge?

Your opponent just riichi'd throwing away the 5-sou. Now, which among these two tiles would you discard? The 8-sou or the 6-sou?

If you answered 8-sou , then congratulations! You have mastered defending using omote-suji! Too bad you just fed into your opponent's hand, a suji trap.

Suji Traps in a Nutshell

Your opponent had a 5-sou, 7-sou, and 9-sou. He discarded the 5-sou to get you to think that 8-sou was a "safe" tile. Because your opponent decided to declare richii with an undesirable center wait, he managed to get a ron.

Suji traps aren't limited to only center waits though. Pair waits, triple waits, edge waits, basically all single waits are viable waits for trapping people with.

The most common way to make a suji trap is to take the commonly used suji knowledge (1-4-7, 2-5-8, 3-6-9) and discard a tile to deceivingly lead into an opponent discarding the winning tile. For example, if you're going to win on a 9-man, discarding the 6-man (preferably with riichi to alert your opponents) will prompt your opponents to start discarding defensively. If they use suji to defend, they will probably discard the 9-man.

Hand:

In the above hand, riichi-ing and tossing the 6M will cause defensive players to consider discarding the 9M.

Suji Traps vs Regular Hands (Tsumo Wins)

Generally one should go for suji traps if one thinks that he/she will not be able to complete the hand with a tsumo.

Do aim for a suji trap if you feel that a certain player is holding your winning tiles.

Do aim for a suji trap if your winning tile has been discarded twice or thrice, so the chances of you drawing it is unlikely.

Do aim for a suji trap if you want to throw your opponents off. The fact that you produced a trap will make them less confident about their "safe" discards

Do NOT aim for a suji trap if the alternative to one is a possible multi-sided wait where getting a tsumo is a high possibility.

Conclusion

To summarize, suji traps are a great way to throw your opponent off and give an alternative way of winning if you can't draw your tile. Do not aim for I though if you have a high chance of getting a tsumo.

Chombo-王

@nevertenpai

(Tiles courtesy of: http://www.martinpersson.org)

Defending Against Damaten?

Let me say this straight out: It's not easy to do.

You can never be certain whether or not someone's in tenpai with a closed hand unless he or she declares riichi. Damaten is one of the unpredictable things in riichi mahjong. That's why people do it in the first place. If fact, a previous post of mine tells the pros and cons of staying in damaten. 

Disclaimer: If you're going to try to defend against a possible damaten, you should accept that you will bail out and likely will not win that hand. Things like breaking a hand to discard a "safe tile" when someone turns out NOT to be in damaten can and will happen. It's up to you to make the decision whether or not you will continue on the offensive or play defensively.

Anyway, so what now? 

Well you will never be sure when someone is in damaten, but you can probably infer from clues and make an educated guess. I already said it earlier, but inferring that the person in tenpai will not necessarily mean that the person is indeed in tenpai. It's poking at probability, but sometimes you might prefer playing defensively over offensively.

What are the possible "clues" I can look for then?

Essentially it all boils down to your opponents discards. That's right, you have to pay attention to their discards even if they don't call. In fact, if you want to be as sure as possible, you have to observe how fast they discard as well. 

Constant tsumogiri 

Tsumogiri or discarding the tile you immediately drew (most web clients like Tenhou show this). If the player keeps on doing this, and in quick succession as well (i.e. upon drawing, the player discards immediately), then it's an indication that one is in tenpai. In addition to damaten, this is one of the only tells you have for determining whether or not people who call tiles are in tenpai. 

The problem with damaten though is that people tend to gloss over their opponents' discards until he or she calls or declares riichi. 

Of course, there will be some cases where this tell would be too late. There are cases where players get ron'd immediately after one person gets into damaten tenpai. Just to keep in mind though, when someone keeps on discarding the tile they drew, you probably should weigh your options and consider bailing out.

Questionable discards

Alone, this isn't and shouldn't be enough, but if you were to combine this with the first tell, you probably can determine whether or not you should be wary of the person. 

For example, A discarded a 5-sou akadora. Now, you have to ask yourself: why would he discard an akadora? Most people would keep akadoras until at least their hand has finished forming. The fact that A discarded an akadora means that his hand is in tenpai. Now, if he continues to tsumogiri afterwards, well the chances of him being in tenpai just shot up.

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So that's basically it. I'll list down additional tells I think also can indicate a damaten, but they probably are not as reliable/more situational/only applies to RL. If you want an additional explanation, you're free to contact me.

Hesitation prior to discarding followed by a tsumogiri 
Discarding two out of three of a set in near succession towards the end/middle of the game
Personal tells (i.e. habits your opponent does after getting to tenpai)

Chombo-王

@nevertenpai