Analysis - Karagiri

 Do you like pointless data? Great! Let's look at karagiri rates in Houou games!

If you don't know what "karagiri" means, it's when you draw a tile that you already have in your hand, then cut that tile from your hand. For example, you draw a 7p, then cut the 7p from your hand instead of the one you drew. Cutting the one you drew is called "tsumogiri." This can have some mind-games attached to it, theoretically, if people are watching your discards.

Anyway, let's begin by simply looking at how often people karagiri at the different shanten numbers. For this, any time a player who isn't in riichi draws a tile that matches a tile in their hand, then discards one of them, it's counted. This analysis was run over 1,539,555 Houou 4-Player Hanchan games.

It has kind of a weird pattern to it. People karagiri the most often at 4-shanten, and the least often at 1-shanten. Karagiri at 0-shanten is also fairly popular.

I looked at karagiri vs tsumogiri riichis as well. I only counted tsumogiri riichis where the player had the choice of doing a karagiri riichi instead. The result was that 50% of karagiri riichis won, while only 45% of tsumogiri riichis won. Why? Who knows. Maybe the karagiri allowed a trap to be set in some way.

Next, let's look at karagiri by number of calls.

These are more even than the shanten numbers. Three calls will usually be tenpai, and it matches up with the 1- and 2-shanten numbers above. The four calls row is a bit funny. There were 50 such cases, which represent people drawing the tile they were waiting on, but not being able to win either due to the score situation or a lack of yaku. A karagiri in this situation would make previously passed tiles unsafe in the eyes of the opponents, but it's also probably obvious you don't have a yaku at that point.

Finally, let's look at the karagiri rates for each individual tile.

Click the image to make it bigger if it's too small to see.

The most commonly karagiri'd tiles are the honours, and the fives. The fives are pretty obvious. If you draw a red five, you will cut the non-red from your hand in almost all cases when choosing between them. Such situations weren't removed from the other data, but it only happens 3/136 times, or 2% of the time. As for why honours, a karagiri honour tile followed by cutting the other looks like a pair drop. Against a riichi this could make it look like you're folding more than you are? I'm just guessing here, I have no idea.

An amusing thing is how the manzu tiles have lower percents than the others. On Tenhou, manzu is sorted to be in the left of your hand. Is mousing over to the left of your hand too much effort? Is it harder to see the opportunity to karagiri when the tiles are so separate? Who knows.

I wonder if karagiri decisions are covered in any popular Mahjong books.