Board & Card Games Stack Exchange is a question and answer site for people who like playing board games, designing board games or modifying the rules of existing board games. It only takes a minute to sign up.
Sign up to join this community
Why is white 4 in this diagram not joseki? How can it be punished by black and how bad is it compared to standard joseki play?
$$ ----------
$$ ..........|
$$ ..........|
$$ ..3.2.....|
$$ ...4..1...|
$$ ..........|
A partial answer is probably: "Because this variation is joseki and it looks more forcing":
$$ ----------
$$ ..........|
$$ ..........|
$$ ..3.2.....|
$$ ..4...1...|
$$ ..........|
I don't think it's that the joseki move is forcing, it's more that the joseki move is better. 5 here is pretty sad for White. For 4 to be joseki, you would need a response to this move that turns out better than the accepted sequence for White.
$$ ----------
$$ ..........|
$$ ..........|
$$ ..3.2.....|
$$ ..54..1...|
$$ ..........|
NOTE: I am stupid and misread your diagram as komoko (3-4) instead of hoshi (4-4) in the corner. The following applies to komoku only! I was going to delete this answer, but then decided to leave it up, because the question would probably be interesting for komoku, too.
W4 is actually joseki, but it is very, very rarely played. I have never witnessed it in high level matches, and I would not at all be surprised if dan players do not know it (the opposite, rather).
I learned it in a book by Yilun Yang (Whole Board Thinking in Joseki). Basically, it is a move that moves white out very steadily (i.e. slowly). Sadly, I do not have the book with me for an extended period of time, but maybe someone else can jump in an add a more detailed explanation of the move.
Either way you don't have to worry about it, really - if your opponent plays W4, deal with it as you would anyway (remember that a non-joseki move can be good sometimes, and also that a joseki move can be bad sometimes, too). If you feel that W4 is a good move on a certain board, don't be afraid to try and play it. You'll see how it turns out!
White 4 gives black another chance to reinforce the corner (at a or b), as it doesn't put much pressure on 3:
$$ ----------
$$ ..........|
$$ ..........|
$$ ..3.2.....|
$$ ...4..1...|
$$ ..........|
$$ ......ab..|
For example:
$$ ----------
$$ ..........|
$$ ..........|
$$ 7.3.2.....|
$$ ..64..1...|
$$ ..........|
$$ ......5...|
The problem with W4 is that it is a "slow," non-forcing move that gives Black many options. Some of those have been covered by other answers, but one good move is P17 (one right of 2) that gives Black the corner, while leaving White very cramped.
If you play a sequence that gives your opponent so many good options, the sequence is probably to your opponent's advantage.
