10

4... Nxb4 is never played on chesstempo database for +2200 players games, being Bxb4 the most popular move.

enter image description here

I don't find any significant change after capturing the pawn with the knight unless after 5. c3, black can play Na6 supporting an eventual c5 to block the a3-f8 diagonal.

If 5...Nc6 it looks the same position as 4...Bxb4 5. c3 Bc5

Stockfish evaluates 4... Nxb4 as =:

enter image description here

Why doesn't this move appear on databases is what I am wondering.

5

It comes down to flexibility. In most cases, Nb4 will end up in the same position, as you said, but Bb4 give you at least two more common alternatives, and a couple less common ones.

 [FEN ""]

 1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. b4 Nb4 5. c3 Nc6 (5...Na6?) 6. d4 exd4 7. cxd4

Compare this with this line where black can play Ba5, Be7, Bc5, and even Bd6 have been played a fair amount of times. It is, generally, favorable to make your opponent worry about more options.

 [FEN ""]

 1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. b4 Bb4 5. c3 
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  • 1
    Is 5....Na6 so bad? As white I use to profit the a3-f8 diagonal if black bishop goes to b6 and Na6 supports c5 – user18196 Dec 22 '19 at 18:27
  • I think just attached the ? by sight since the N does nothing for anything on a6. After plugging it in to Stockfish, it agrees totally as 6.Nxe5 is +1.81 after Qg5 7. d4 Qg2 8. Rf1 and it is really bad. – PhishMaster Dec 22 '19 at 18:32
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    Oo yup dismised 6.Nxe5 is free thx – user18196 Dec 22 '19 at 18:46
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    It is already over +3 for white there, and the only move is Nf6; Bf7 Kf8; Bb3, and there is nothing there that will convince me that is fun to play for black. You cannot even dislodge the Ne5 with d6 f4! since taking you cannot move the N due to 0-0 winning. – PhishMaster Dec 22 '19 at 19:01
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    But the knigth at a6 should not help the counteratack. Sorry for not checking it was a +2 position – user18196 Dec 22 '19 at 19:05
3

In my database it actually appears in 131 games, or roughly 1.5%.

The move also isn't objectively bad. But it's unpopular partly because it unnecessarily limits Black's options. After 4...Nxb4 5.c3, Black is practically forced to play 5...Nc6, which transposes to 4...Bxb4 5.c3 Bc5 (as you mentioned). Meanwhile, after 4...Bxb4 5.c3, Black has many options (5...Ba5, 5...Be7, 5...Bd6, or 5...Bc5).

There's also the issue that 4...Nxb4 looks unnatural. The knight should generally stay on c6 where it guards the key centre squares e5 and d4. Finally, some people might think allowing 5.Nxe5 is much better for White, even though it actually gives Black a winning advantage after 5...Qf6!.

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    Isn't this basically exactly what I said in my answer and the comments with the exception of quoting the stats? – PhishMaster Dec 23 '19 at 3:01
  • @PhishMaster I also mentioned stats, the knight staying on c6 to guard squares, and the issue of some people thinking 5.Nxe5 is good for White. I didn't copy your answer when writing mine. – Inertial Ignorance Dec 23 '19 at 3:03
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    Even if you did not intend to, you still did. Your main idea is almost word for word what I wrote. You should read the other answers before answering. The comments to the other answer also go over Ne5? in depth. It was not cool at all. – PhishMaster Dec 23 '19 at 3:14
  • @PhishMaster I don't see how my main idea is word for word whatsoever, please point out which sentence you're referring to. If you mean the 5th moves I mentioned for Black, I found them by looking at the top choices in a correspondence database. I mentioned Ne5 because at first I thought it was good, and A. N. Other also thought it was best. ...Qf6 was found immediately with my engine, not by using your comment. – Inertial Ignorance Dec 23 '19 at 4:04
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    I wrote that quickly at night on a phone: I should have said idea for idea ("limits black's options="flexibility"; "(5...Ba5, 5...Be7, 5...Bd6, or 5...Bc5)"="Compare this with this line where black can play Ba5, Be7, Bc5, and even Bd6 have been played a fair amount of times."; and "5.Nxe5 is much better for White, even though it actually gives Black a winning advantage after 5...Qf6!."=the comments "That just loses to Qf6 since the Ne5, Qf2 mate, and the Ra1 all hang. The best line then is 6. 0-0 Qe5 7. c3 Bd6 8. g3 (f4 Qc5+ and Bc4 hangs) Nc6 and keeps the piece." Still, looks too close. – PhishMaster Dec 23 '19 at 12:32
1

After 4...Nxb4 5.Nxe5 looks like a very strong reply, gaining the important e5 Pawn almost for free and posing an immediate threat to f7.

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  • 6
    That just loses to Qf6 since the Ne5, Qf2 mate, and the Ra1 all hang. The best line then is 6. 0-0 Qe5 7. c3 Bd6 8. g3 (f4 Qc5+ and Bc4 hangs) Nc6 and keeps the piece. – PhishMaster Dec 22 '19 at 20:11
  • P.S. I am not one of the people, who downvoted since I just assumed you would delete this answer. – PhishMaster Dec 23 '19 at 0:02
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    No worries. I never thought you downvoted my answer, but you can do that, if you feel so. I’ll keep it as a reminder of how easy it is to make a mistake. I didn’t see 5...Qf6. As simple as thay. – A. N. Other Dec 23 '19 at 6:13
  • I still rarely downvote an answer, and still have not for this one. – PhishMaster Dec 23 '19 at 12:27
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    It seems that 4...Nxb4 might be an option in view of the "trap" 5.Nxe5 Qf6. Of course after 5.c3 Nc6 Black is committed to the ...Bc5 line. At this point, I'd play 5.0-0 as White, rather than 5.c3. – A. N. Other Dec 23 '19 at 13:04

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