In a video I'm watching (requires register), with this setup,

King can't castle

the instructor says

The king cannot escape, he cannot castle king side or queen side, because of the white's pressure on e7 [...]. Black wants to escape this pressure by castling by hand.

I don't understand why can't black castle. It won't castle from, through, or into check. Why is it?

  • 1
    Black certainly can castle for both sides, but if he does... you know that Qxe7 Qxe7 followed by Rxe7 winning the knight as well. White gaining material advantage afterwards. – Tetsuya Yamamoto Oct 3 '17 at 15:08
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    He just means you better not castle. – johnny Oct 4 '17 at 17:34
  • In other words, the king should not escape or castle to either side, because it would mean giving a queen and knight (and if he castles queenside, a pawn, for after Qxe7 Qxe7 Rxe7 Black can't defend both... Rxb7 and ... Rxg7) for a queen. – Monty Harder Oct 4 '17 at 19:11

Executive summary:

Black actually can castle, but if he does castle he will lose the knight and the game (due to material loss).

Detailed answer:

Black and White have equal material.

  • The black knight is protected by two pieces: the king and the queen.
  • The black knight is attacked by two pieces: the queen and rook.

If the king castles, the knight will be protected only by the queen, and White will be able to win the knight which will lead to a big material advantage: a knight, which is worth about 3 points.

"Castle by hand" (meaning moving the king and the rook over several turns until they reach a castle position) will allow Black to keep protecting the knight. (E.g. By moving the king to F7 to protect the knight, followed by a rook to E8, etc.)

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    Ok, so it wouldn't be illegal, just a bad idea because white would lose a knight, correct? – garci560 Oct 3 '17 at 10:44
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    @nprensen - correct - this is my understanding. – Yaron Oct 3 '17 at 10:44
  • @nprensen - did I answer your question? – Yaron Oct 3 '17 at 12:11
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    @nprensen Except if the king has been moved earlier in the game, then you're not allowed to castle. Or if a rook has been moved earlier, then you cannot castle with that rook. But that's probably not the case in this game. – Paul Oct 4 '17 at 13:11
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    @ThorbjørnRavnAndersen From Wikipedia: "Neither the king nor the chosen rook has previously moved." – Paul Oct 4 '17 at 20:54

There is one possibility when castling would be illegal - if king has moved earlier in the game - then the move would be illegal.

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  • Welcome to Chess Stack Exchange! While this is correct in general, this does not apply to the question at hand. – Glorfindel Oct 4 '17 at 11:45
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    This is the famous game Wilhelm Steinitz vs Curt von Bardeleben, 1895. Black hasn't moved the king before the position shown in the game. – user1108 Oct 4 '17 at 13:37
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    You cannot move your king over a check to castle either. – johnny Oct 4 '17 at 17:35

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