Kabe

Kabe 「壁」 (lit. "wall", also called "blockade") is a defensive tactic that takes into account the number of tiles available.

• If you can see all four copies of that tile, an opponent can never have that tile.
• If you can see multiple copies of a tile, then an opponent is less likely to have that specific tile.

When multiple/all copies of a tile are visible, the same-suit tiles towards the outside (away from 5), and up to +/-2 away, become safer.

Visible tiles

"Visible tiles" are tiles you can see, and thus know aren't in an opponent's hand. These include:

• Tiles in the discards
• Tiles in the dora indicator(s)
• Tiles in your own hand
• Tiles used for your opponent's tile calls

For example, a call for kan reveals all 4 copies of a tile, which can immediately be used for kabe.

Defense

Kabe does not make a tile 100% safe, but it can help determine which tiles are less likely to deal in.

No chance

No chance occurs when all four tiles of a tile are visible, which means that no copies of that tile can be hidden in an opponent's hand. This makes certain hand compositions become impossible. Therefore, tiles towards the outside (up to +/- 2 away) become safer.

For example, if all four 3-pin are visible, it is impossible for an opponent to have 3-pin, making it impossible for an opponent to have a wait pattern of:

Pattern	Waiting for

Overall, when all copies of 3-pin are visible:

• and are much safer than normal, since it's impossible for an opponent to have a ryanmen or kanchan wait on those tiles.

• and are only a bit safer than normal, since an opponent can have a ryanmen wait (56-pin or 67-pin in hand) on those tiles. They are still quite dangerous.

Kabe works on tiles towards the outside, up to +/- 2 away from the all-visible tile. E.g., if all four 4-pin are visible, 2-pin and 3-pin are safer but 1-pin is not.

Kabe can be combined with other kabe or suji to eliminate ryanmen waits. For example, with all four 3-sou and 7-sou visible, 5-sou is safer. Similarly, if all four 4-pin are visible and an opponent discards 9-pin, the 6-pin is safer against that opponent. (There are two possible ryanmen waits for 6-pin: 45-pin and 78-pin. A 45-pin in hand is impossible due to kabe, while a 78-pin in hand would be furiten due to the 9 discard).

One chance

One chance occurs when three copies of a tile are visible. The concept works like no chance: when three copies are visible, then it is less likely (but still possible) for an opponent to have the fourth copy hidden in their hand. For example, if you can see three copies of 3-pin, then 1-pin and 2-pin are less likely to be an opponent's winning tile.

A one chance tile is less safe than no chance, but still safer than a regular tile in the early- to mid- game. However, it is no longer safe in the late-game because it's not unlikely that the opponent has the last copy of that tile.

Double one chance

Double one chance occurs when three copies of two adjacent tile types are visible. For example, if three 3-pin are visible and three 2-pin are visible, double one chance applies to 1-pin. Double one chance is less safe than no chance but safer than once chance.

Safety

No chance is as safe or safer than suji, since no chance prevents ryanmen and kanchan waits, while a suji tile is only immune against ryanmen waits. In addition, kabe applies to all players, while suji only works on specific players. However, since kabe is relatively rare, both defensive techniques should be considered.

One chance tiles are less safe than suji. One chance becomes dangerous in the late game, since it becomes likely for an opponent to have the last copy of a tile.

Like suji, kabe implies that an opponent has a ryanmen (or kanchan) wait. So if an opponent is going for a hand like toitoi or chiitoitsu, the usual rules of kabe don't apply. Instead, if you are certain an opponent has a pair/triplet wait, like if they have a hadaka tanki, rely on tiles that have all 4 copies visible.

Tile Efficiency

While "kabe" usually refers to the defensive practice, looking at the visible tiles is important for tile efficiency.

By counting the number of visible copies of a tile, you can deduce how likely a certain tile group is to form. For example, when two of a type type are visible, then no other player can form a triplet. This particularly applies with honor tiles. The same logic may be applied to sequences; e.g. as 3-man tiles become visible, completing a 12-man penchan becomes less likely.

Thus, it may hinder a player's hand from reaching tenpai, winning, or having certain yaku. This is particularly the case for yakuman. In the case of kokushi musou, if all four of a tile type required for that yakuman, then the possibility for any player completing the hand is completely nullified.