Threat Assessment

18.1 Identifying Dangerous Opponents

Threat assessment is the skill of evaluating how dangerous each opponent is at any given moment. Not all opponents are equally threatening, and your defensive effort should be proportional to the threat level. A player who declared riichi on turn 6 with an unknown hand is a clear, high-priority threat. A player who has been discarding normally with no calls is a lower-priority threat (though never zero—dama tenpai exists).

18.2 Riichi as a Threat Signal

Riichi is the strongest threat indicator because it explicitly announces tenpai. When an opponent declares riichi, you know with certainty they are tenpai. The timing of their riichi provides information about their hand: early riichi (turns 5-8) suggests a fast, efficient hand that may have good waits. Late riichi (turns 12+) suggests a hand that struggled to develop, possibly with a worse wait but potentially with more accumulated value.

18.3 Open Hand Threat Signals

Open hands broadcast information through their visible melds. A player who has pon'd two dragon sets is very likely pursuing a high-value hand (possibly shou san gen or even dai san gen). A player who has chi'd three times in one suit is likely building chinitsu or honitsu. The more calls a player makes, the fewer tiles remain in their concealed hand, and the closer they are to tenpai. With three open melds, a player has only 4 concealed tiles—they may be tenpai or very close.

18.4 Discard Reading for Threat Level

Opponents' discard patterns reveal their hand direction. A player discarding many honor tiles early is probably building a simples-heavy hand (tanyao, pinfu). A player who discards manzu and pinzu tiles while calling in souzu is building a souzu-based hand. A player whose discards suddenly shift from one suit to another may have changed their hand plan, possibly drawing into a different structure.

18.5 Estimating Hand Value

When deciding whether to push or fold (Module 19), you need to estimate not just whether an opponent is tenpai but how much their hand is likely worth. Key indicators:

Open yakuhai hands: Minimum 1 han (yakuhai). If they have dora visible or the dora indicator is favorable, could be much more.

Riichi hands: Minimum 1 han (riichi). With ippatsu and ura dora potential, expected value is typically 3-4 han average.

Honitsu/Chinitsu hands: Visible from suit concentration in discards. Honitsu is 3 han closed, chinitsu is 6 han closed—these are high-value threats.

Dora count: If you can see few dora copies in discards and your hand, the opponent may hold them. More invisible dora = higher expected threat value.

18.6 Threat Assessment from Riichi Timing

The turn on which an opponent declares riichi provides significant information about their hand. Analysis of Tenhou data reveals patterns:

Early riichi (turns 5-8): The opponent had a fast hand — likely good tile efficiency in their starting hand. Their wait is more likely to be ryanmen (because efficient development tends toward two-sided waits). Expected hand value: moderate (2-3 han base, potentially higher with dora). These hands are dangerous because they have many remaining wall draws to complete.

Mid-game riichi (turns 9-12): Standard timing. The opponent's hand developed at a normal pace. Wait quality is variable. This is the most common riichi timing.

Late riichi (turns 13+): The opponent struggled to reach tenpai. Their wait may be worse (more likely kanchan, penchan, or tanki). However, their hand may have accumulated value through dora or yaku built during the long development. Late riichi hands are less likely to win (fewer remaining draws) but may be more expensive if they do win.

This timing analysis, discussed in Kawada Jiro's (川田浩之) statistical articles, provides a prior estimate of the threat before any specific discard-reading is applied. Combining timing analysis with discard reading gives a much more accurate threat assessment than either alone.

18.7 Threat Assessment for Open Hands — Visible Information

Open hands broadcast far more information than closed hands, making threat assessment easier but the threats themselves no less real. A specific analytical framework, taught by Doi Takeshi (土井泰昭) in his calling-strategy materials:

Count the open melds: 1 open meld = opponent has 10 concealed tiles. 2 open melds = 7 concealed tiles. 3 open melds = 4 concealed tiles (likely tenpai or very close). 4 open melds = 1 concealed tile (definitely tenpai, tanki wait).

Identify the yaku: Visible pon of yakuhai = guaranteed 1+ han. Visible chi in one suit + honor discards = likely honitsu. Multiple pon of terminals/honors = likely honroutou or similar.

Estimate the value: Visible yakuhai + estimated dora + visible suit concentration → rough han estimate. An open hand with pon of haku + pon of chun + discards showing manzu/souzu concentration = very likely shou san gen candidate (4+ han minimum), an extremely dangerous hand.