With all that being said, defense against an apparent toitoi begins by narrowing down the possible yakus of the hand. The 1st pon eliminates all the yakus that require a closed hand. Calling on an end tile or honor tile obviously eliminates tanyao. The 2nd pon eliminates hands based around chi. Pons on 2 different suits eliminate honitsu/chinitsu. Tenpai for toitoi specifically isn’t possible until the 3rd call, and by that point you’re usually looking at either yakuhai, tanyao, toitoi, or no ten. Sometimes you’ll see 3 pons on a single suit or a single suit and honors, pointing to honitsu/chinitsu as well. With that in mind, read the discards accordingly. Toitoi waits on a very low number of tiles, either a dual pon wait or a single wait, so you’ll usually find that you have more than enough safe tiles to make it through the game. Furiten tiles are obviously safe. Tiles that have atleast 2 used up are safe from toitoi before the 4th pon. Honitsu/chinitsu eliminates 1 suit from the safe area, and tanyao/yakuhai waits can be determined through suji. Other than that, avoid dealing the dora or tiles around the dora when it could be tied into the hand.

As mentioned above in the article, the weakness of calling is that it restricts the hand, not only the yaku it can make, but the number of safe tiles it has to deal against threatening hands. One of the ways to attack toitoi is to use up it’s winning tiles and then riichi. Since toitoi focuses on speed, opponents usually value tiles that allow a hand to progress quickly, and aim for tiles that haven’t already been discarded or called. Tiles that already have 1 or 2 used up tend to flow out of the hand. This makes which tiles an opponent is likely to have and likely to cut predictable. Tiles that hold the most possibilities are usually held onto the longest, while isolated tiles are cut more quickly, with honor tiles usually being some of the last useless tiles to be cut, usually after 1-2 calls, and then the menzi. By predicting the areas where an opponent’s waits will be, you can either incorporate their waiting tiles into your hand or build your own waits around the same tiles. Riichi pressures the opponent into eventually making stronghanded deals or taking apart their own hand. Another way to attack toitoi is by placing restrictions on what tiles they can deal by hinting at strong hands with calls.

Finally, if no other options are available, chosing to deal into a cheap hand to avoid someone completing a monster hand is a prudent strategy. i.e. if an opponent is in apparent tenpai with a toitoi, honitsu, yakuhai hand and little to none of the dora have been discarded yet, your own hand is still progressing, and another player has an open tanyao or yakuhai hand.

One last thing to mention, and the first to consider when playing, is the strength and mentality of the opponent. Suji, discard, and hand reading require a context in order to yield useful information. That context is the opponent (and the flow of the game). Against high level opponents that can use tricky and unusual waits effectively (refer to Akagi and Ten for examples), as well as read into your own hand and mentality, normal strategies lose a lot, if not most, of their power. Good luck if you find an opponent like this.

I’ve been actually closer to Suu An Kou and Dai San Gen. At least suu an kou is not that obvious…

Unless they’re going for a fat kokushi.

For chiitoitsu… already discarded tiles seem to come to me a lot faster than undiscarded tiles. >o>