is 1 , open or closed. An opponent adds a fourth tile to one of their pons to make a , and that tile is your winning tile. You call on it, and the kan never happens.
The Japanese is 槍槓. This site's glossary lists it as Robbing the Kan, and the EMA 2016 rules call it Robbing the kong.
Which kans you can rob
An . On their own turn, the player adds the fourth tile to a they called earlier. The EMA 2016 rules treat that tile as a discard you can claim for a win.
An called on a discard isn't on the list. You had your chance at that tile when it was discarded.
A closed kan can't be robbed, with one exception: thirteen orphans. The EMA 2016 rules and Mahjong Soul allow it. Tenhou doesn't.
It counts as a ron
The robbed tile is a ron, and the EMA 2016 rules say so. A adds the 10 fu for a closed ron, and menzen tsumo never applies. Furiten stops it like any other ron.
The kan isn't completed, so no turns over. The EMA 2016 rules say that too.
A closed hand
This closed hand waits on 
or 
, from both sides. Four runs and a pair of 8 pin make it pinfu. An opponent with a pon of 6 sou draws the fourth one and adds it.
You call ron. That's chankan and : 2 han 30 fu. A collects 2,000. The dealer collects 2,900. On an ordinary discard, the same 6 sou would be pinfu alone: 1,000, or 1,500 for the dealer.
Now say you'd declared on this hand, and the added kan came before your next draw. Riichi, ippatsu, chankan, and pinfu make 4 han 30 fu. A non-dealer collects 7,700. The dealer collects 11,600. That's the table value: without kiriage, 4 han 30 fu doesn't round up to a .
An open hand with no other yaku
You called on 123 sou: 
. These ten tiles are still in your hand.
The hand waits on only, a . It has no yaku. The 1 sou and the 9 man rule out , and the chi rules out every closed-only yaku. A discarded 5 pin can't win.
An opponent with a pon of 5 pin adds the fourth. Chankan is your yaku. The fu are the base 20, plus 2 for the middle wait, and an open hand gets no 10 for a ron. 22 rounds up to 30. At 1 han 30 fu, a non-dealer collects 1,000. The dealer collects 1,500.
Those payments have no , no , and no riichi sticks. The scoring guide counts fu like these line by line.
Thirteen orphans and a closed kan
This hand waits on only. An opponent who holds all four 1 man calls a closed kan.
The EMA 2016 rules and Mahjong Soul let you rob it. That's a : 32,000 for a non-dealer and 48,000 for the dealer. On Tenhou the kan goes through, and you can't win on it.
Tenhou, Mahjong Soul, and EMA 2016
Tenhou's rules list 槍槓 at 1 han, with no mark for a closed hand. They say can't win on a tile from an opponent's closed kan. They say and chankan combine on the first of two kans in a row. By the second, the first kan has already ended the ippatsu window. Pass on a chankan and Tenhou makes you until your next draw.
Mahjong Soul's Japanese FAQ defines chankan as a ron on the tile an opponent declares for an added kan, and adds that thirteen orphans can rob a closed kan.
The EMA 2016 rules agree with Mahjong Soul on thirteen orphans. They count the win as a ron and turn over no kan dora.
The glossary entry is the short form: a ron on the tile used to upgrade a pon to a kan.
Common mistakes
- Trying to rob an open kan called on a discard. Only an added kan can be robbed.
- Robbing a closed kan with a normal hand. Only thirteen orphans can, and not on Tenhou.
- Adding . Chankan is a ron.
- Dropping ippatsu. A robbed kan never happens, so it doesn't end the window.
- Counting the kan dora. The kan wasn't completed.
- Passing it and calling ron later in the same go-around. On Tenhou, you're furiten until your next draw.
What sits with it
Riichi, ippatsu, pinfu, tanyao, and anything else the tiles hold. Never menzen tsumo, rinshan kaihou, or : those are tsumo wins.
Price a chankan
The score calculator turns 2 han 30 fu, chankan with pinfu, into 2,000 or 2,900. On an ordinary discard, the same hand is 1 han.
Open the score calculator