hi,
i am quite new in opening theory. so my questions might sound really stupid. i apologize for that.

now my questions:
1. in the evan's gambit, if black plays 4...Nxb4 instead of 4...Bxb4, what should be white's answer? is that a bad move by black? why? or why not?

2. in the ruy lopez, what if black plays 4...b5 immediately after 1. e4 e5; 2. Nf3 Nc6; 3. Bb5 a6; 4. Ba4
what should the white's answer be after he plays 5. Bb3 ? i mean how should he approach the game after 4...b5 ?

One less-popular defense to the Evans gambit is:

1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.b4 Bxb4 5.c3 Bc5. This is generally thought to give black less winning chances than the more common ...Ba5 variations.

If black plays 4.Nxb4 c3 then 5.Nc6 just returns to that main line, and ...Na6 is clearly just worse.

In the Ruy, by playing ...b5 right away black avoids the delayed exchange variation. However, he's now two moves from castling and the bishop is targeting f7.

That opens up a new possibility for white: playing it as a two knights: 5.Bb3 Nf6 6.Ng5!? d5 7.ed Nd4. Or even 6.d4 ed 7.e5.

There's also the thematic 5.0-0 and 6.a4, where you're turning the b-pawn in a weakness earlier. This may transpose, and it certainly limits black's choices (eg, he can't now play 5.0-0 Bc5 and play the underrated Moller defense without b5 becoming a critical weakness).

The ultimate evaluation of these positions is beyond my abilities. It's not clear that any of them are worse for black than the deferred exchange variation (which is many popular among weaker players for it's surprise value) but they're interesting attempts to mix up the position.

I'm not an expert on these openings, but I'll try to answer anyway. I'm sure stronger players will correct anything I'm wrong about.

1. About 4. ... Nxb4 in the Evan's Gambit:

After 4. ... Nxb4, black's e5 pawn is no longer protected, so white could just play 5. Nxe5, getting back the gambit pawn and double attacking the f7 pawn. I'm looking at this position and I keep looking at insane attacking possibilities for black, like 5. ... Bxf2+, 5. ... Qf6, or 5. ... Qg5 instead of the more boring and defensive 5. ... Nh6. Actually, now that I think about it, I think that Qg5 looks like the most tempting, but I don't have time for detailed analysis right now. I can see it coming out similar to Blackburne's Shilling Gambit. Unfortunately for black's attacking chances, that knight on b4 isn't in a position to help with a king side attack. At first glance, I thought white was clearly winning, but the more I think about it, the more I think that this position is weird and tactical enough that it might actually be fun to play, even if it is inferior. It's tactical enough to be dangerous for both sides.

As another option white can play the immediate 5. d4, since the d pawn will be protected twice and attacked twice. This is more forcing against 4. ... Nxb4 than it would be against 4. ... Bxb4, because the d4 pawn will attack the bishop on c5.

On the other hand, getting opponents out of their opening preparation is
sometimes enough of an advantage to make up for such weaknesses, especially at low-intermediate levels.

I just checked the 2 million game database at chesslab.com, and it looks like most of the 13 games with 4. ... Nxb4 continued 5. c3 Nc6, transposing back to a mainline of the Evan's Gambit. Blackburne played 5. 0-0 d6 6. c3 Nc6, and went on to win as white.

2. About the Ruy Lopez with 1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 b5 5. Bb3:

At this point, white's bishop is attacking f7, so if black brings out his knight to f6 (or e7), white can play Ng5 as if it was the Two Knights Defense, but with the advantage of a safer bishop position.

That's why I don't play 4. ... b5 as black, anyway. I want to bring out at least one of my king side pieces before the bishop goes to that diagonal. For instance, 1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. 0-0 and now b5 is safer for black. If 5. ... b5 6. Bb3 Be7 7. Ng5, then black simply castles and his f7 pawn is protected by the rook.

And no, you shouldn't take it anyway (7. ... 0-0 8. Bxf7+ Rxf7 9. Nxf7 Kxf7). Many beginners think that a rook and pawn are equal in value to a knight and bishop (5+1 = 3+3, right?), but it doesn't work out that way. I've read that the standard value of minor pieces being worth 3 pawns is off. They're worth closer to 3.25 pawns, so that makes a knight and bishop worth more than a rook and pawn. So black's ahead materially after that line, with a better position because of his developed knights and pawns giving him a space advantage.

I still usually don't play b5 that early, but at least I know that after I've played Nf6, I do have that option.

Hope this helps. Hopefully, some of the better players will add their 2 pawns worth...

--Fromper

"And no, you shouldn't take it anyway (7. ... 0-0 8. Bxf7+ Rxf7 9. Nxf7 Kxf7). Many beginners think that a rook and pawn are equal in value to a knight and bishop (5+1 = 3+3, right?), but it doesn't work out that way. I've read that the standard value of minor pieces being worth 3 pawns is off. They're worth closer to 3.25 pawns, so that makes a knight and bishop worth more than a rook and pawn. So black's ahead materially after that line, with a better position because of his developed knights and pawns giving him a space advantage."

I don't think nitpicking about piece values really gets to the point, here. Generally, you'd rather have the two pieces than a rook and pawn, but the bigger issue is that white is trading off his only two developed pieces. You have to winning a substantial amount of material to put yourself in a position where you have no developed pieces (although he has castled) whereas black has two.

For examples of games go to chesslive.de.
There are several examples on site, the earliest 1904.

I did mention in the last sentence of that paragraph that black's ahead positionally as well as the slight material advantage. Given how many beginners make this mistake because they just think of everything in terms of material "values", I figured it was worth pointing out. I'm not sure if the original poster would make this mistake, but others reading this might benefit from having this stuff pointed out.

--Fromper

After 5.Nxe5 it seems to me that black has worse problems than he usually does in an Evans gambit and he isn't even up a pawn as compensation! Black has to do something about the threat 6.Bxf7+ or 6.Nxf7 with a fork on the rook and queen. Black also has to be careful as a defensive move like 5...Nh6 doesn't work because of the check on h5 with the queen at the end of the trades on f7 picking up the bishop on c5 and attacking the knight on b4.

1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.b4 Nxb4 5.Nxe5 Nh6 6.Nxf7
( 6.c3 Nc6 7.Nxf7 Nxf7 8.Bxf7+ Kxf7 9.Qh5+ g6 10.Qxc5 )
6...Nxf7 7.Bxf7+ Kxf7 8.Qh5+ g6 9.Qxc5


Often white can just transpose into regular lines. Usually this move order is used to avoid the ruy lopez delayed exchange deferred variation which goes on the theory that black has misdeveloped two pieces when compared to the regular exchange variation.

How white approaches the game after 4...b5 will depend on how black follows up. Often play can transpose back into main lines or take on a life of its own.

Crash

This is dangerous for white as black can play a gambit with d7-d5 and Nc6-d4 which has black a tempo up on another gambit line where white plays the same knight move after white castles and black plays d7-d6. The line is quite playable for black without the extra tempo. I have played this in over the board play with some success.

Crash

I recall Soviet players playing the Ba4 b5 5. Bb3 Na4 line in the 60's.
Chessbase has 2000 games in the database. From 1845 to 2000.
The question is, is the line playable for Black. Probably Yes.
The following is a game from 1963:
[Event "USA-ch"]
[Site "New York"]
[Date "1963.12.15"]
[Round "7"]
[White "Addison,William"]
[Black "Fischer,Robert James"]
[Result "0-1"]
[Eco "C70"]
1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 b5 5.Bb3 Na5 6.d4 exd4 7.Qxd4 Ne7 8.c3 Nxb3
9.axb3 Bb7 10.Bf4 d5 11.e5 c5 12.Qd3 Ng6 13.Bg3 Be7 14.Nbd2 Nf8 15.0-0 Ne6 16.Rad1 g5
17.h3 h5 18.Rfe1 Qb6 19.Nf1 d4 20.N3d2 g4 21.h4 Qc6 22.Qe4 0-0-0 23.Qxc6+ Bxc6 24.c4 Kd7
25.Ra1 Ra8 26.Ne4 Bxe4 27.Rxe4 Ng7 28.Nd2 Nf5 29.Rf4 Ke6 30.Ne4 bxc4 31.bxc4 Rhb8 32.Ra2 Rb4
33.Nd2 Nxh4 34.Bxh4 Bxh4 35.Re4 Bg5 36.f4 gxf3 37.Nxf3 Be3+ 38.Kh2 Rxc4 0-1
Fischer on the White side faced the line a year later and won. See below.

Three games by Larry Evans:
[Event "Capablanca mem"]
[Site "Havana"]
[Date "1964.??.??"]
[Round "3"]
[White "Smyslov,Vassily"]
[Black "Evans,Larry Melvyn"]
[Result "1/2"]
[Eco "C70"]
1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 b5 5.Bb3 Na5 6.0-0 d6 7.d4 exd4 8.Nxd4 Bb7
9.Bd2 c5 10.Bd5 Bxd5 11.exd5 cxd4 12.Qe1+ Qe7 13.Bxa5 Qxe1 14.Rxe1+ Ne7 15.Nd2 Kd7 16.Nb3 d3
17.c3 Nxd5 18.Rad1 Re8 19.Rxe8 Kxe8 20.Rxd3 Nf4 21.Rd1 Ne6 22.Nd4 Nxd4 23.cxd4 g6 24.Rc1 Bg7
25.d5 Bxb2 26.Rc7 Kf8 27.Rc6 Ke7 28.Bb4 Be5 29.Rxa6 Rc8 30.g3 1/2

[Event "Capablanca mem"]
[Site "Havana"]
[Date "1964.??.??"]
[Round "5"]
[White "Garcia Martinez,Silvino"]
[Black "Evans,Larry Melvyn"]
[Result "0-1"]
[Eco "C70"]
1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 b5 5.Bb3 Na5 6.0-0 d6 7.d4 exd4 8.Nxd4 Nxb3
9.axb3 Bb7 10.c4 b4 11.Re1 Qd7 12.Nd2 Ne7 13.Nf1 g6 14.Ne3 Bg7 15.Nd5 0-0 16.Bh6 Nxd5
17.Bxg7 Ne3 18.Rxe3 Kxg7 19.Ra5 Rad8 20.Rg5 c5 21.Ne2 Rfe8 22.Ng3 Kh8 23.Rg4 Qe6 24.Rf4 f6
25.Qf3 Rf8 26.h4 Qe5 27.h5 g5 28.Rf5 Qxb2 29.h6 Qa1+ 30.Kh2 Bc8 31.Rd5 Be6 32.Rd1 Qe5
33.Red3 a5 34.R1d2 a4 35.Qd1 axb3 36.Qxb3 Rf7 37.Ra2 g4 38.Ra6 Qf4 39.Kg1 Rfd7 40.Rd1 Qxh6
0-1

[Event "Capablanca mem"]
[Site "Havana"]
[Date "1964.??.??"]
[Round "13"]
[White "Pachman,Ludek"]
[Black "Evans,Larry Melvyn"]
[Result "1/2"]
[Eco "C70"]
1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 b5 5.Bb3 Na5 6.0-0 d6 7.d4 exd4 8.Nxd4 Bb7
9.Bd2 Nxb3 10.axb3 g6 11.c4 c5 12.Nf3 b4 13.Bf4 f6 14.Re1 Qc7 15.Nbd2 0-0-0 16.Nf1 Ne7
17.Ne3 Bg7 18.Nd5 Nxd5 19.cxd5 Rhe8 20.Nd4 Rd7 21.Ne6 Qb6 22.Qg4 Bh8 23.Bh6 Rde7 24.Bf8 Rd7
25.Bg7 Bxg7 26.Nxg7 Ree7 27.Ne6 Kb8 28.Re3 Ka7 29.Rae1 Rf7 30.Rf3 f5 31.exf5 Bxd5 32.fxg6 Bxf3
33.gxf7 Bxg4 34.f8=Q Qb8 35.Qf6 Qg8 36.f3 Bh5 37.Nf8 Bxf3 38.Qxf3 Rf7 39.Qc6 Qxf8 40.Ra1 Kb8
41.Re1 Ka7 42.Ra1 Kb8 43.Qxa6 Kc7 44.Qc4 Re7 45.h3 Qe8 1/2
Fischer on the White side:
[Event "Houston sim"]
[Site "Houston"]
[Date "1964.??.??"]
[Round "0"]
[White "Fischer,Robert James"]
[Black "Heising,C"]
[Result "1-0"]
[Eco "C70"]
1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 b5 5.Bb3 Nge7 6.Ng5 d5 7.exd5 Nd4 8.Nxf7 Kxf7
9.d6+ Nxb3 10.dxe7 Bxe7 11.axb3 Bb7 12.0-0 Rf8 13.Nc3 b4 14.Ne2 Qd5 15.f3 Kg8 16.Ng3 Qd4+
17.Kh1 Bd6 18.d3 Qh4 19.Ne4 Rf5 20.Be3 Raf8 21.Bf2 Qh6 22.c4 g5 23.Qe2 Qg6 24.c5 Be7
25.d4 Qe6 26.dxe5 Qxe5 27.Bg3 Qe6 28.c6 Qxc6 29.Rac1 Qe6 30.h3 c5 31.Rfe1 R8f7 32.Qd2 Qd5
33.Qc2 Qc6 34.Qc4 a5 35.Rcd1 Ba6 36.Qc2 Rd5 37.Rxd5 Qxd5 38.Nf2 Bf8 39.Ng4 Qf5 40.Qc1 h6
41.Re8 Kh7 42.Qe3 Qb1+ 43.Kh2 c4 44.Rxf8 Rxf8 45.Qe7+ Kg6 46.Qxf8 Qxb2 47.Ne5+ 1-0

thanks to everybody for all the help. further help is definitely welcome.

Malbase, among the games you mentioned, white won in only one game. is that because of poor play or a weakness of the variation used.