This is day one of the 66th Honinbo title match Yamashita Keigo (W) vs. Hane Naoki (B)

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I'm thinking...

Did anyone else find the diamond shape created with move 15 kind of odd?

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I'm thinking...

Not odd in the sense that it's a pretty common shape. It goes back to Yasui Chitoku but it has been very popular in the past few years.

However, I admit to feeling it leans towards overconcentration, so it may be a stylistic option rather than best play in absolute terms.

It may also be a "Chernobyl group", a GoGod term of which I'm quite fond.
Black has created a solid group in an area where White has committed more stones. He has score for action on the lower side, and can now activate his stone in the top left without fear of a splitting attack.

Or maybe it's just stylistic...who can tell with pros.