What is the least common move？

What is the least common move？

O-O#, maybe?

Probably something like gxh8=B#.

https://www.chess.com/blog/smurfo/the-most-unusual-move-in-chess-or-quothow-i-won-a-beer-in-my-lunch-breakquot

That should be about right. For a second I wondered if it was even legally possible.

Oh, I'm in a lot of threads.

Hmm... that's actually pretty interesting. I think your're right - Kh8# isn't possible - but I'm not 100% sure.

Actually no, it is:

?

Oh, I see.

Some en passant move might compete.

I wonder,

can anybody find a way that O-O++ or O-O-O++ is legal?

Or prove that it is not?

Ra7 in defense of b7

no he means O-O-O double check

0-0-0 with double check is almost certainly impossible, as it would require a piece on the back rank to reveal a check from a piece behind it...

Which is impossible since double check involves a discovery, and castling cannot be a discovery since it is on the edge of the board and therefore there cannot be a piece behind the king/rook to give a discovered check when the king/rook moves.

resign

Castling twice (apparently did happen once).

Reference: Greatest number of castlings.

Least common move is Ba1-h8 (or any of its 3 counterparts, Bh8-a1, Bh1-a8, or Ba8-h1).