Defense
Defense in Japanese mahjong focuses on one important concept: avoiding other players' hands, by not discarding winning tiles. Other concepts rests on not giving other players any tiles needed to call. This aspect of the game is greatly emphasized during other player(s)' riichi declarations and/or threat of high scoring hands. Regardless, it is in the best interest for players to avoid losing points directly to other players, as much as possible.
General overview
Defense is part of the game's learning curve. Typically, beginner players may not be aware of defensive play, due to greater focus devoted towards general hand development and memorization of yaku. In the early stages of the learning curve, players may consider the prospect of generating points from developing hands as a means of procuring winning games. In most other activities, this pretense is true. Eventually, players learn the importance of minimizing point losses, especially via ron. Point losses via tsumo or ryuukyoku are minimal, and they're easily reclaimed with relatively easy winning hands. Especially in the case of tsumo, point losses are shared among all the players, rather than one bearing the brunt of the entire opposing hand's point value. In many instances, points lost rather than points gained during the game determines the outcome for a player. Of course, a player still has to produce hands in order to maintain contention.
Safe tiles
Japanese mahjong offers players the ability to determine, deduce, and infer safe tiles. This is all with the help of the discard piles of all players; but in particular, other players may show threats, like riichi declarations or open hands showing some kind of large hand.
Anpai
Defense focuses on anpai 「安牌」, or safe tiles. Safe tiles are discarded tiles, that cannot be called for ron. So to effectively employ defensive tactics, players must take into account of all four discard piles and the furiten rule. All tile that are visible to a player are those in one's own hand, the discard pile, any called tiles, and dora indicators.
Genbutsu
The most important technique. Thanks to the furiten rule, any tile that an opponent has discarded is 100% safe against them. The temporary furiten rule makes tiles discarded on the current go-around 100% safe against players who haven't had their turn after the discard. The riichi furiten rule makes all tiles discarded after riichi safe against that riichi.
The ways of defense and offense
Betaori
Betaori focuses on discarding nothing but safe tiles. In this state, a player has completely abandoned all hope of developing a winning hand; and instead, the hand is dedicated towards avoiding any threatening hands. At times, even a player achieving a tenpai hand may need to completely break the tenpai for avoidance. The essence of betaori is to always discard the safest tile first. Suji tiles or even hell wait only honors shouldn't be discarded before any genbutsu tiles.
Uchi-mawashi
Uchi-mawashi is a half-way style where a player aims to discard fairly safe tiles while still aiming for tenpai. Discardable tiles include honors, suji tiles and no-chance kabe tiles. From this state a player may fall back to betaori upon drawing dangerous tiles, or attack when reaching tenpai. This style is not recommended for beginners, and should be used rarely. It is appropriate to use when in a good shape iishanten for a strong hand.
Kanzen Shinko
The way of complete offense. A player basically ignores the opposing tenpai and proceeds to attack normally. It can be used with a very strong hand, a situation where a win is required, or in any case where the hand contains very few safe tiles. In the last case, one can switch to betaori if tiles in the hand become safe.
Techniques to find safe tiles
Genbutsu
The most important technique involves identifying safe tiles, particularly the guaranteed ones. Due to the furiten rule, any tile that an opponent has discarded is 100% safe against that particular opponent. The most effective safe tile are the ones 100% safe against all of them. The temporary furiten rule makes tiles discarded on the current go-around 100% safe against players who haven't had their turn after the discard. With this, a tiles from kamicha (player to the left) are temporarily safe, if not claimed for a win. Discarding the same tiles as other players for defense, that technique is called awaseuchi 「合わせ打ち」.
Honors
Honor tiles are generally safe, since they are hard to wait on. Tiles that have already passed are much safer than live ones. Guest wind tiles are both safer and less damaging than yakuhai tiles. Live yakuhai should be considered fairly dangerous. When three of one type is discarded, then the fourth is guaranteed safe, because it is no longer usable in anyone's hand.
Suji
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Suji focuses on taking advantage of the furiten rule, and its application to the mahjong octaves. Most good waits wait on tiles in the same suji. For example, if a player has discarded 4-pin, the 1-pin and 7-pin are safe if the opponent has a ryanmen wait. Neither is perfectly safe, however, and the 7-pin is much more dangerous than the 1-pin. This is because the 1-pin can only complete a shanpon or tanki wait, while the 7-pin can also complete a penchan or kanchan wait. A discarded 8-sou does not make the 5-sou safe, but if both 8-sou and 2-sou are discarded, the 5-sou is suji. The order of suji safety is 19>double-suji 456>28>37.
On the other hand, this strategy may actually work backwards, when suji is actually used to bait players into discarding tiles that appear to be safe. Suji tiles of tiles discarded after riichi are safer for this reason, while tiles discarded right before riichi and when declaring riichi are the most dangerous. It is common to riichi discarding 6 from 246 to bait out the 3. Players also declare riichi with bad waits, and suji is useless against them. Relying only in suji to defend will result in many play-ins. Suji should be used when genbutsu tiles have ran out, or in Uchi-mawashi.
Kabe
A tactic similar to suji that uses "walls" formed by seeing all 4 of a tile to remove the possibility of ryanmen waits. For example, if you see all 4 of 6-man, no player can have a 56-man or 67-man shape, so a ryanmen waits for 7-man and 8-man are impossible. Like suji, other waits are still possible, but note that a 68-man wait for the 7-man is also blocked, making the 7-man safer than a 4-man discard suji. Kabe safety is comparable to suji safety, and should be used in similar fashion.
External links
- Basic Defense Techniques in Mahjong