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I was analyzing a recent game of mine, and I noticed something interesting. After I blundered back a bishop on move 16, the evaluation was -3.4, which is still strongly winning for Black.

[White "White"]
[Black "Black"]
[Result "0-1"]
[WhiteElo "1700"]
[BlackElo "1500"]
[fen ""]

1. e4 c5 2. f4 { B21 Sicilian Defense: McDonnell Attack } b6 3. Nf3 Bb7 4. Nc3 a6 5. Bc4 e6 6. O-O d5 7. exd5 exd5 8. Be2 d4 9. Ne4?? { (-1.03 → -4.31) Blunder. Nb1 was best. } Bxe4 10. d3 Bb7 11. Ng5 Be7 12. Bf3 Nc6 13. Re1 Nf6 14. Qe2 O-O? { (-5.42 → -3.17) Mistake. Qd7 was best. } 15. Bxc6 Bxc6 16. Qxe7 Qd5 17. Nf3?! { (-3.25 → -5.04) Inaccuracy. Qe2 was best. } Rae8 18. Qc7 Rxe1+ 19. Kf2? { (-4.63 → -19.29) Mistake. Nxe1 was best. } Ree8 20. Qxb6 Ng4+ 21. Kg3 Ne3 22. Qb3 Nf5+ 23. Kf2 Qd7 24. Bd2 Bxf3 25. gxf3 Nh4 26. c4 Qh3 27. Qd1 Qxh2+ { White resigns. } 0-1

How is this so, given that the material had evened out? Obviously, if it's not due to material, it must be due to something positional, but even then I'm not very convinced. After move 16, White owns the e-file and maybe even the 7th rank. They also has a knight on g5 which, to me, is a bit worrisome (should it not be?), and it's supported by a pawn and a bishop. What merits such a strong evaluation for Black?

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    I haven't analyzed - but it feels to me like White eventually has to give up something to prevent Qxg2 mate, especially given that they have trouble bringing their second rook into the game. – Alexander Woo Nov 28 '20 at 23:47
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White's actually quite close to busted in that position after 16...Qd5. Of the two points you bring up, note that White doesn't actually control the e-file because Black is ready to play a rook to e8 and drive White's major pieces away. The knight on g5 looks good, but it's also vulnerable to being kicked by ...h6 and it's not threatening anything yet. Otherwise, White's king is dangerously exposed on the long diagonal since Black already has a bishop on the diagonal and since White no longer has f3. Finally, White's queenside is undeveloped. Granted Black's a8-rook isn't developed either, but it can jump into the fray much quicker.

Consider, checkmate is threatened on g2 and White has only a few ways to defend it:

  • 17.Re2 is the easiest to refute because 17...Rfe8 wins either a rook or the queen.
  • 17.Nf3 is also terrible. Again Black plays 17...Rfe8, and after 18.Qc7 (or where else is White going to put the queen?) Black plays 18...Rxe1 19.Nxe1 (forced) 19...Rae8 (developing with tempo) 20.Nf3 (still forced) Re2. Black's pieces are overwhelming White's king while White's queen, bishop and rook are all spectators. An immediate threat is 21...Rxg2+ 22. Kxg2 Qxf3 and checkmate.
  • That leaves 17.Qe2, which is the least evil but still not good enough. Black again plays 17...Rfe8, forcing 18.Ne4 (all other moves either lose material or get mated on g2), and then the Knight is pinned. Black has a variety of promising ideas such as 18...Qf5 intending to take on e4, or 18...Nd7 intending ...f5 to win material.

By the way, it's striking how much of Black's advantage stems from the fact that White's queenside is undeveloped, and by extension the rook on e1 is undefended (once ...Rfe8 kicks the queen away). Move White's c1-bishop to d2, and Black's advantage drops to about -1.0.

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It seems that, for tactical reasons, White is going to have to give up material to stop Black's attack with best play from both sides. That seems to be why the evaluation is so in favor of Black.

After move 16, White owns the e-file and maybe even the 7-rank.

Not really. After 16...Qd5, White must defend the mate threat somehow, and Black can then play a rook to e8 to drive the queen off of it (as was done on the game). White's undeveloped bishop also delays the other rook from helping, and that's critical in some lines - if that bishop were on d2 instead of c1 at move 16, Black's advantage would be very small. As it is, it's really Black who soon owns the e-file.

He also has a knight on g5 which, to me, is a bit worrisome (should it not be?)

It could be kicked easily with h6, and h7 and f7 are defended, so it's not all that worrisome. (Especially since White doesn't get the 7th rank to attack f7 from the side with rooks.) In any case it's going to be moving soon to help deal with Black's attack even if it isn't kicked. There's no way it can stay where it is; for example after 17.Qe2 Rae8 it has to move because 18.Qf2?? Rxe1+ loses immediately.

Beyond that, White's bishop is doing next to nothing and is blocked by the f4 pawn, while Black's is aiming right at White's king on the long diagonal. Black has more queenside space. There's a hole on e3 that Black could put his knight into (if he doesn't mind it being traded for the bishop) or he could just put it on g4 (Black can kick it with h3, but that would leave a permanent hole on g3.)

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