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[FEN ""]
[startply "16"]
[StartFlipped "1"]

1. e4 d6 2. Bc4 Nf6 3. Nc3 g6 4. d3 Bg7 5. Nf3 Nc6 6. O-O e5 7. Ng5 O-O 8. Bxf7+ Rxf7 9. Qf3

Why does the engine go from -1.5 to -8.5 after the queen move? There isn't an opportunity to trap the queen yet and the black is only two points ahead in material. My guess is that the queen walks into a discovered attack by the rook and the queen can be immediately attacked with Nd4. I played Rf8 afterwards to keep my rook on the f file. The top engine line is just to move the queen back to where it came from and then the knight is kicked out too.

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13
  • 2
    Why didn't you take the rook? And It's losing for Nd4 and Bg4.
    – Billy Istiak
    Commented Dec 25, 2022 at 2:37
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    @BillyIstiak I played as black (idk how to flip the PGN) I don't know why White didn't take back
    – qwr
    Commented Dec 25, 2022 at 2:40
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    black is only two points ahead in material Engines are waaaay past the time when their evaluations reflected the material on the board. Plus, these days most engines index their evaluations to chance of victory.
    – Allure
    Commented Dec 25, 2022 at 13:48
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    @DM lichess's stockfish 14+ NNUE at depth 26 lichess.org/analysis/standard/r1bq2k1/ppp2rbp/2np1np1/4p1N1/4P3/…
    – qwr
    Commented Dec 25, 2022 at 13:51
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    @Allure That's good to know, but that's in the notes for version 15.1, which is a higher version that what was used here, so it probably wouldn't apply here.
    – D M
    Commented Dec 25, 2022 at 14:07

2 Answers 2

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9

White is a piece down for just a pawn in this position. Taking the rook would give them a reasonably balanced position, but by refusing to take they get a totally lost one.

There are also some ideas with Bg4 and Nd4 that speculate with trapping the queen or taking on c2 (potentially forking the rook and queen if she moves to the wrong square).

I wouldn't pay too much attention to the specific number. Whether it's -3 or -7 it doesn't matter much. The fact is that White should have taken the rook and any other move is a blunder.

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1
  • 1
    Another detail coming out bad for White: The knight g5 can't safely retreat, on f3 it will be pinned (the Q only has d1 as safe field) and on h3 exchanged. Thus White, in addition to material woes, also has a trashed castling position.
    – Hauke Reddmann
    Commented Dec 25, 2022 at 20:36
5

It seems like white played Bxf7, and after Rxf7, instead of taking the rook with Nxf7, white played Qf3. Now black -among others- can play the simple Rf8 and are a piece up for a pawn.

The fact that the advantage is so large just depends on the engine and its version. For example, from Stockfish 15.1 evaluations are not that extreme (in my laptop it's "only" -5).

In any case, white position goes from -1 to completely lost not because Qf3 puts the queen in danger or anything like that, but just because they didn't play Nxf7 (winning a rook for a knight), sort of balancing the material on the board.

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