Defense Fundamentals
17.1 Why Defense Matters
Defense (守備, shubi) in riichi mahjong is the skill of avoiding dealing into opponents' winning hands. A single deal-in (放銃, houjuu) can cost thousands of points and devastate your placement. Strong defensive play is often what separates intermediate players from advanced ones. In Japanese mahjong analytics, reducing your deal-in rate (放銃率, houjuu-ritsu) is one of the most impactful improvements a player can make.
17.2 Betaori (ベタオリ) — Full Defense
Betaori (ベタオリ, "flat fold") is the act of completely abandoning your hand to play pure defense. You stop trying to improve your hand and focus entirely on discarding tiles that are safe against opponents' winning hands. Betaori is appropriate when: (a) an opponent declares riichi and your hand is far from tenpai, (b) multiple opponents are threatening, (c) the risk of dealing in far outweighs the reward of winning, or (d) you are protecting a good placement (e.g., in first place in the final round).
17.3 Safe Tile Categories
Genbutsu (現物) — 100% Safe Against Specific Player
Tiles that a specific player has already discarded are guaranteed safe against that player. Because of the furiten rule, a player cannot be waiting on any tile they have previously discarded. Genbutsu is the only truly 100% safe tile category. When folding against a specific riichi player, their genbutsu are your safest discards.
Suji (筋) — Statistically Safer
Suji is a defense technique based on the logic of ryanmen (two-sided) waits. If a player has discarded 4m, then a ryanmen wait involving 4m is impossible. Since a 2m-3m ryanmen waits on 1m or 4m, and 4m is in discards, the 1m side of that ryanmen is not a threat. Similarly, since 5m-6m waits on 4m or 7m, the 7m side is safe against that ryanmen. Therefore, if 4m has been discarded, both 1m and 7m are "suji" against that player.
The suji relationships are: 1-4-7 and 2-5-8 and 3-6-9 within each suit. If the middle tile of a suji group has been discarded, the outer tiles are safe against ryanmen waits.
Suji is NOT 100% safe. It only eliminates ryanmen waits. The opponent could still be waiting on a suji tile through other wait types: kanchan, penchan, shanpon, or tanki. Suji reduces the probability of dealing in but does not eliminate it. Japanese strategy sources typically estimate suji as roughly 80-90% safe against a typical riichi hand, depending on the specific situation. Never treat suji as equivalent to genbutsu.
Kabe (壁) — Wall Block
Kabe ("wall") refers to the situation where all four copies of a tile are visible (in discards, your hand, or open melds). If all four copies of 5p are accounted for, then no ryanmen involving 5p exists (neither 3p-4p nor 6p-7p). This makes certain adjacent tiles safer. Kabe is a powerful defensive technique because it eliminates specific waits with certainty.
No-Chance (ノーチャンス)
If all copies of a tile that would be needed to form a wait are visible, the wait is impossible. For example, if all four 3m are visible, then no one can have a 1m-2m penchan wait or a 2m-4m kanchan wait. The specific "no-chance" conditions depend on what tiles are visible and what waits they eliminate.
One-Chance (ワンチャンス)
If three of four copies of a key tile are visible, only one copy remains. A wait requiring that tile is possible but unlikely (only one way to complete it). One-chance tiles are safer than average but not as safe as no-chance or genbutsu.
17.4 Defensive Discard Priority
When folding, prioritize discards in approximately this order:
1. Genbutsu of the threatening player (100% safe)
2. Shared genbutsu (tiles discarded by multiple players, safe against all of them)
3. No-chance tiles (safe based on tile visibility)
4. Suji tiles of the threatening player (high but not perfect safety)
5. One-chance tiles (reduced but not eliminated risk)
6. Honor tiles not in the threatening player's discards (low but nonzero risk)
7. Tiles with kabe support
8. Central tiles of suits with unknown status (most dangerous—avoid if possible)
17.5 Common Defensive Mistakes
Blindly trusting suji: Suji is not 100% safe. Over-reliance on suji without considering the full board leads to avoidable deal-ins against kanchan, shanpon, and tanki waits.
Ignoring non-riichi threats: Defense is not only relevant against riichi players. Open hands with visible yakuhai triplets can be just as dangerous. Dama tenpai players are threats too—even though you don't know they're tenpai.
Late defense: Waiting too long to fold. If you recognize you cannot realistically win and an opponent is threatening, fold immediately rather than pushing "one more tile" and dealing in.
QUIZ — Question 17.1
An opponent declared riichi. Their discard pool includes 4s. You need to discard and are choosing between 1s and 5s. Which is safer against this specific opponent?
Answer: A. The suji groups for souzu are 1-4-7, 2-5-8, and 3-6-9. Since 4s is in the opponent's discards, the 1-4-7 suji is active: both 1s and 7s are suji-safe against ryanmen. The 5s belongs to the 2-5-8 group, which requires 2s or 8s in discards to be suji-safe. Without 2s or 8s in discards, 5s has no suji protection and is more dangerous.
17.6 Defense in Practice — A Complete Betaori Sequence
Let us walk through a complete defensive sequence from a beginner game. You are at 2-shanten when an opponent declares riichi on turn 8. Your hand:
(Plus two tiles in open melds from earlier calls.)
Opponent's discards: 4z, 2z, 1m, 8m, 3s, 6p, [riichi on 6p sideways].
Step 1: Identify genbutsu. Safe tiles against this opponent: 4z, 2z, 1m, 8m, 3s, 6p. Check your hand — do you hold any of these? You hold 3s (genbutsu!) and 1z, 3z (not in their discards, but honor tiles).
Step 2: Plan discard sequence. Discard 3s first (genbutsu, 100% safe). Next: 1z (guest wind honor — not genbutsu but relatively safe; honors are only dangerous against tanki or shanpon waits). Then 3z. Then look for suji: opponent discarded 1m, so 4m is suji (1-4 suji) — you hold 4m. Opponent discarded 8m, so 5m is suji — but you do not hold 5m.
Step 3: Execute. Discard order: 3s → 1z → 3z → 5z → 4m (suji) → then you are running low on safe tiles and must assess remaining options carefully.
This systematic approach — genbutsu first, then honor tiles, then suji — is the standard defensive sequence taught in all Japanese defense instructional materials, including the defense-focused chapters of 『現代麻雀技術論』(Gendai Maajan Gijutsu-ron) by Nagai Takanori (長井隆典).
17.7 The "Suji Trap" — Why 100% Trust in Suji Kills You
A critical warning that appears in every serious Japanese defense text: suji is NOT 100% safe. The suji safety rate against a typical riichi hand is approximately 85-90%, meaning roughly 1 in 8-10 suji discards will deal in. Over many hands, this adds up. If you discard 3 suji tiles per defensive hand across hundreds of hands, you will occasionally deal in on suji.
The tiles that suji does NOT protect against include: kanchan waits (e.g., suji says 1m is safe because 4m was discarded, but the opponent could be waiting on 1m via a shanpon or tanki wait), shanpon waits (pair-based waits that do not follow ryanmen logic), and tanki waits (single-tile pair waits). Murakawa Yousuke (村川洋介), a professional known for his defensive prowess, has noted in commentary that distinguishing between suji-safe and genuinely safe situations requires reading the opponent's hand pattern — not just mechanically applying suji.
Source notes: Defensive concepts (suji, kabe, genbutsu, no-chance, one-chance) are standard in all Japanese mahjong instructional materials. Safety probability estimates for suji are based on statistical analyses of Tenhou game data. The priority ordering presented here is consistent with standard Japanese defense pedagogy.