2024/05/18 DPA: "A Lead Shield Stops X-Rays"
White to move.
[Full disclosure: This is not a real-time analysis since it's my puzzle submission.]
Black has a potential back rank weakness. White's defense looks shaky but the Rook covers the back rank and the Knight and the Knight covers f2 and the Bishop covers f1 and g2.
The obvious Queen sac 1. Qxe8 is wrong because it assumes Black will recapture 1. ... Rxe8 2. Rxe8#.
But Black has 2 defenses: 1. ... Rg8 and 1. ... Ra8 [X-Ray defending the Rook through the Queen].
The White Knight can't move due to 1. ... Qxf2+ 2. Kh1 Qxh2#.
And if the Rook leaves the back rank, 1. ... Qxd1+, which, admittedly isn't checkmate but there's nowhere for the Rook to go that furthers the attack.
1. Qd7 is an idea, to pile up on the Knight but Black then gets to play 1. ... Nf6, removing the target, attacking the Queen, and defending the Rook.
This is such a great defensive move that White must either prevent it or find a way to make it irrelevant.
That way is 1. Qf7:
- 1. ... Nf6 2. Qxf8+ Ng8 3. Re8 and checkmate is inevitable after Black exhausts his checks
- 1. ... Rxf7 2. Re8+ Rf8 3. Rf8#
- 1. ... Rg8 2. Rxe8 Qxd1+ 3. Bf1 Ra8 [hoping for 4. Rxg8 Rxg8] 4. Qxg8#
.
The position after 3. ... Ra8 is instructive: 4. Rxg8 looks equivalent to 4. Qxg8 since, in either case, the checking piece is protected by the other piece. But the former is a mistake because Black's Rook X-Ray defends the g Rook through the White Rook [dashed red arrow]:
4. Rxg8+?? is met by 4. ... Rxg8.
Instead, White uses his Rook as a barrier to protect his Queen against the X-Ray defense.
What stops X-Rays? A Lead Shield.
I didn't see this term in the chess lexicon [Dane Mattson hadn't either] so I invented it. Most people would think of this as an Interference but there's a critical difference: Interference involves actively placing a piece to block a defense [like yesterday's 1. Bb6, blocking the Black Queen's defense of the Rook].
The Lead Shield keeps the barrier piece in place [in this case, the Rook] and uses another piece to attack the X-Ray defended target [Black's g Rook].
Hat tip to @BryanCFB for brainstorming a name for the idea.
https://www.chess.com/blog/EnPassantFork/the-lead-shield
In the actual game. Qxe8 was winning [and what I played] but it wasn't optimal. Dane changed certain aspects to make Qf7 the only winning move.
https://www.chess.com/game/live/104208004059
.
As is often the case, there are multiple, checkmate-delaying moves the opponent can make, including saccing both Queen and a Rook, but none alter the outcome. The solution at least offers a chance that White might blunder and capture with the Rook instead.