user9531: In this Lichess puzzle, after the initial moves
[title "Black to move"]
[fen ""]
[Startply "17"]
[StartFlipped "1"]

1. c4 b5 2. cxb5 Bb7 3. Nf3 g5 4. Nxg5 Bg7 5. Nf3 c5 6. Nc3 a6 7. d4 axb5 8. Nxb5 Qa5+ 9. Nc3 Bxf3!

Why can the bishop just take the knight? Why is it so bad for white to retake on f3?

user15221: After you complete the puzzle, "
Stockfish 14+NNUE
in local browser" appears in the upper right (just above the list of moves), and a toggle button appears to the right of that. If you click it, it will suggest the continuation 10. Bd2, but you can play around with other lines by making those moves on the board. For instance, after 10. gxf3, the engine recommends 10. ... cxd4. As it has been captured, the knight is not available to capture the pawn, and the queen is deterred by the bishop on g7. As the knight is pinned, it can't be moved away.

user18809: After retaking the bishop, Black will take on d4 with his pawn, attacking the pinned knight. White can do nothing to stop Black from capturing it "for free" on the next move.

user4418: Here's why:
[FEN "rn2k1nr/1b1pppbp/8/q1p5/3P4/2N2N2/PP2PPPP/R1BQKB1R b KQkq - 1 1"]

1...Bxf3 2. exf3 cxd4 3. Bd2 (3. Qxd4 Bxd4) dxc3 4. bxc3 Bxc3 5. Rc1 Bxd2+ 6. Qxd2 Qxd2+ 7. Kxd2 Rxa2+ 8.Ke3 Nc6

White is completely lost.

9531: <p>In this <a href="https://lichess.org/training/Y4tuf" rel="noreferrer">Lichess puzzle</a>, after the initial moves</p>
<pre><code>[title &quot;Black to move&quot;]
[fen &quot;&quot;]
[Startply &quot;17&quot;]
[StartFlipped &quot;1&quot;]

1. c4 b5 2. cxb5 Bb7 3. Nf3 g5 4. Nxg5 Bg7 5. Nf3 c5 6. Nc3 a6 7. d4 axb5 8. Nxb5 Qa5+ 9. Nc3 Bxf3!
</code></pre>
<p>Why can the bishop just take the knight? Why is it so bad for white to retake on f3?</p>
 15221: <p>After you complete the puzzle, &quot;
Stockfish 14+NNUE
in local browser&quot; appears in the upper right (just above the list of moves), and a toggle button appears to the right of that. If you click it, it will suggest the continuation 10. Bd2, but you can play around with other lines by making those moves on the board. For instance, after 10. gxf3, the engine recommends 10. ... cxd4. As it has been captured, the knight is not available to capture the pawn, and the queen is deterred by the bishop on g7. As the knight is pinned, it can't be moved away.</p>
 18809: <p>After retaking the bishop, Black will take on d4 with his pawn, attacking the pinned knight. White can do nothing to stop Black from capturing it &quot;for free&quot; on the next move.</p>
 4418: <p>Here's why:</p>
<pre><code>[FEN &quot;rn2k1nr/1b1pppbp/8/q1p5/3P4/2N2N2/PP2PPPP/R1BQKB1R b KQkq - 1 1&quot;]

1...Bxf3 2. exf3 cxd4 3. Bd2 (3. Qxd4 Bxd4) dxc3 4. bxc3 Bxc3 5. Rc1 Bxd2+ 6. Qxd2 Qxd2+ 7. Kxd2 Rxa2+ 8.Ke3 Nc6
</code></pre>
<p>White is completely lost.</p>
