St Andrew's Cross
(Diagonal Double Pin Attack)

In Chess, a Diagonal Double Pin Attack is often referred to as the St Andrew's Cross, with its main feature resembling that of the diagonally, double crossing lines on the Scottish flag.

Battle Log - Header Graphic
  1. Qg2 ... Qh1#
  2. 0-1

Historical Game:
Capablanca-Alekhine, World Chess Championship, 1927

In the actual World Chess Championship match, the move you see in the video clip didn't actually happen - Capablanca (White) foresaw his inevitable loss and Resigned after 68 Moves ...

However, if he'd have played on, White would have had to make the Block with his
d-file Queen ...

On Black's next move, those present would have witnessed a Diagonal Double Chess Pin, which took its name after the Scottish flag, with its two diagonal white lines.

So ...

Move 67, White would have set the first diagonal Pin - an Absolute Pin - by sending his d-file Queen down to g2, in order to Block the current "Check" by Black's f1 Queen.

However, that Queen of White's would be doomed to remain, unable to move, as long as Black's f1 Queen remains on that square ...

This she does and Black would simply move his other Queen to h1, to complete the second diagonal Pin ...

This time, it's a Relative Pin - against White's g2 Queen, which would be protecting the other White Queen, on a8.

White's King would have nowhere to escape, as Black's h5 Pawn is guarding the only other exit square (g4) ...

And, without help from any other piece, it'd naturally be "Checkmate" (#) - a Win for Black (0-1).

From The St Andrew's Cross Diagonal Double Pin,
Check Out Some Basic Chess Pin Attacks
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