A wasted move, so long as black doesn't abandon c7, allowing the fork.
The Queen ought to be happy on b6 or d8, protecting the c7 square, and keeping her majesty to the dark squares where typical Scandi light-square development a la c6 both frees her to move about unhindered and chases away the knight with tempo.
The opponent is just hoping for a cheap tactic. Nothing to fear. Melts doesn't even bother to give the line a mention in his Qd6 book.
There was a guy in our club that played Qd6 variation all the time. I got draws and loses against him each time I kept developing my pieces normally, because I started sacrifising pieces way too much (can't stand defensive players. can't do anything against them but giving away my warriors one after another for a single hope of cracking defenses up...). I tried Nb5 twice against him and actually managed to win both of those games, because he always tended to check me after I hit his queen with my horse. That way I developed my forces even faster and he couldn't prepare his defence in time and I've beaten him up. To sum up - I think Nb5 is a playable variation, especially if your opponent thinks he can get your monarch with a lonely lady right in the opening.
I played a player that's quite short-tempered, so I knew he wouldn't resist a chance to attack my queen, even it's a single stupid check. That's called psychology. I no longer play that way, by the way. That was in 2011.
I don't know if Black's position is good after
White seems to have an advantage here. What is an ideal plan for Black? I was thinking ...Nf6, ...g6, ...Bg7 trying to hit the wide open centre.
First of all, I think 4... Qd8 is the correct move. Then, standart c6, e6 and other Wall Building and black is fine. In your variation, white has a knight developed, but a somewhat weak pawn on a5. Black has a pawn on c6 that's blocking his pony from it's natural square. Black should just castle as soon as possible (Nf6, g6, Bg7, O-O seems fine) and then think how to develop his queenside, maybe later pushing the c pawn for some fight of the center. Those are my ideas. I haven't really read anything about Scandinavian Qd6, so it's possible I may be wrong, but my current ideas are those mentioned above.
In my opinion Nb5 is a (small) mistake. The queen is not well placed on d6. So just ignore it. Unless you fall asleep and somehow get mated at h2 I can't see what its going to do there. So leave it be. The refutation of a bad move is often not an immediate tactical flurry. Note that there may be a critical tempo gain in playing Ne4 or Nb5 at some point. Most likely the queen will have to move again.
Sun Tzu said "do not attack when your enemy is crossing the river - the danger (for him) in crossing is sufficient advantage (for you)". The chess-related point is that once you attack its easy for your opponent to find moves - one that doesn't lose immediately is probably best. But lay back and watch him flounder. Keep your eye on the prize - in the opening that is to place a pawn in the center (e4 or d4), get your minor pieces out (knights to c3, f3) bishops anywhere (that doesn't drop one), castle, queen moves, rooks to open files or center files. NO wasted moves. This is a bit trite of course, but if you keep in mind that this is what you SHOULD be doing, while paying attention to the tactics moves like Qd6 won't put you off your game.
In the present case you could continue your development with d4. I think this is better than Nf3 which may not prevent e5 and makes his move easy (Bg4). Note if he trys 4) ... e5 in response to 4) d4 then 5) Nb5 has more bite than before. It still is not necessarily a good move - moving the same piece twice gets your knuckles rapped by Dr. Tarrasch who was a pretty good player. However, to hold both e5 and c7 he would need to play Qe7 (Ok - so I am dreaming, but I have seen worse moves - even made them from time to time). Then 6) Nf3 and if he is the kind of person who plays Qd6 why not exd4+. Then Be2 followed by oo. What's not to like? Can you see the threats? One idea is Re1 pinning the queen. Another is Bg5 with a possible mate with Qd8. Yes there are pieces in the way right now but these are just some possibilities (along with Bf4 and Nc7). You have a significant lead in development almost a winning advantage in itself.
Good luck
In my opinion Nb5 is a (small) mistake. The queen is not well placed on d6. So just ignore it. Unless you fall asleep and somehow get mated at h2 I can't see what its going to do there. So leave it be. The refutation of a bad move is often not an immediate tactical flurry. Note that there may be a critical tempo gain in playing Ne4 or Nb5 at some point. Most likely the queen will have to move again.
Sun Tzu said "do not attack when your enemy is crossing the river - the danger (for him) in crossing is sufficient advantage (for you)". The chess-related point is that once you attack its easy for your opponent to find moves - one that doesn't lose immediately is probably best. But lay back and watch him flounder. Keep your eye on the prize - in the opening that is to place a pawn in the center (e4 or d4), get your minor pieces out (knights to c3, f3) bishops anywhere (that doesn't drop one), castle, queen moves, rooks to open files or center files. NO wasted moves. This is a bit trite of course, but if you keep in mind that this is what you SHOULD be doing, while paying attention to the tactics moves like Qd6 won't put you off your game.
In the present case you could continue your development with d4. I think this is better than Nf3 which may not prevent e5 and makes his move easy (Bg4). Note if he trys 4) ... e5 in response to 4) d4 then 5) Nb5 has more bite than before. It still is not necessarily a good move - moving the same piece twice gets your knuckles rapped by Dr. Tarrasch who was a pretty good player. However, to hold both e5 and c7 he would need to play Qe7 (Ok - so I am dreaming, but I have seen worse moves - even made them from time to time). Then 6) Nf3 and if he is the kind of person who plays Qd6 why not exd4+. Then Be2 followed by oo. What's not to like? Can you see the threats? One idea is Re1 pinning the queen. Another is Bg5 with a possible mate with Qd8. Yes there are pieces in the way right now but these are just some possibilities (along with Bf4 and Nc7). You have a significant lead in development almost a winning advantage in itself.
Good luck
I think the OP was asking how to play from this position as black not as white. Gary Lane's book "Ideas behind modern chess openings: black" covers the 3. ...Qd6 Scandinavian although I'm not sure that it covers 4. Nb5
Qd6 has had the GM seal of approval for like 20 years now. The "kind of person" who plays Qd6 is rated over 2600 a lot of the time these days.
I've actually never thought of 4...Qd8 before and I think its decent as White now does not have a reason to push a4.
Note that if White plays 5.bf4, double attacking c7 black can either go Nd5 or Na6, and play c6 next to kick out the knight
Thanks for feedback.
There are much better ways of chasing Black's queen. For instance after 1. e4 d5 2. exd5 Qxd5 3. Nc3 Qd6 4. d4 c6?! 5. g3 preparing not just the K-side fianchetto but also Bf4, is practically a refutation. Similarly after 4...Nf6 5. Bc4!? c6?! 6. Nge2 Black is faced with the unpleasant threat of Bf4
Just backtracking a little, in your diagram, after 5.a4, you could probably play 5...a6 instead of 5...c6.
Qb6 and Qd8, Qe6+ looks like a dubious move but worth trying to catch opponent off guard and play a very interesting game.
There are much better ways of chasing Black's queen. For instance after 1. e4 d5 2. exd5 Qxd5 3. Nc3 Qd6 4. d4 c6?! 5. g3 preparing not just the K-side fianchetto but also Bf4, is practically a refutation. Similarly after 4...Nf6 5. Bc4!? c6?! 6. Nge2 Black is faced with the unpleasant threat of Bf4
You might want to inform GM Sergei Tiviakov that his beloved Qd6 Scandi is "practically" refuted. As a former practitioner of the Qd6 Scandi myself, I just want to point out that the main line against your suggested moves is 4...Nf6 5.Bc4 a6 where Nge2 is pointless. 5...a6 prepares b5, kicking the bishop and allowing for Bb7. I've played it many times in blitz.
I didn't claim 3...Qd6 is refuted but rather 4. d4 c6? after 5. g3. And I didn't claim 6. Nge2 should be played after 4...Nf6 5. Bc4 a6 but rather after 5...c6? I was just trying to point out White has other more effective means of chasing Black's ...Qd6 than 4. Nb5?!
Nevertheless after 5...a6 6. Nf3 b5?! 7. Bd3 Bb7 8. Qe2 is more than pleasant for White:
black
I didn't claim 3...Qd6 is refuted but rather 4. d4 c6? after 5. g3. And I didn't claim 6. Nge2 should be played after 4...Nf6 5. Bc4 a6 but rather after 5...c6? I was just trying to point out White has other more effective means of chasing Black's ...Qd6 than 4. Nb5?!
But you listed black playing the moves 4...c6 and 5...c6 when those aren't even black's main line theory. It seems to me if you're going to claim "there are much better ways of chasing the black queen" that you'd start with the moves black is most likely to play. Otherwise, the point you were trying to make falls short as I pointed out.
Also in your example game (which makes use of players much lower rated than Tiviakov), correct theory for black is 8...e6 first as 9.Ne4 doesn't work there. So 8.Qe2 e6 9.0-0 Nbd7 and if 10.Ne4, then 10...Qc6 11.Nxf6 Nxf6 and black is perfectly fine. Additionally in your example game, black just about blundered with 9...Qb6? when 9...Qd5! was the correct move.
"you listed black playing the moves 4...c6 and 5...c6 when those aren't even black's main line theory" and the lines I give demonstrate why. Just play the correct 4. d4 instead of 4. Nb5?! and Black has ample opportunity to go wrong and allow White to chase his queen around.
"your example game (which makes use of players much lower rated than Tiviakov" This is chess.com FCOL -- practically everybody is lower rated than Tiviakov. They are also almost all rated lower than the 2300+ FIDE players in the game I featured as well.
Anyway as for "So 8.Qe2 e6 9.0-0 Nbd7 and if 10.Ne4, then 10...Qc6 11.Nxf6 Nxf6 and black is perfectly fine." and White has the thematic 12. a4, which on the 11th move also leaves White standing better after your suggestion "in (my) example game, black just about blundered with 9...Qb6? when 9...Qd5! was the correct move" after 10. Nxf6 whichever way Black re-captures.
I'm sure Tiviakov would do much better from the White side of these positions than the Black side. And if his ICCF rating was 600 points higher than his FIDE rating, he could market himself as the Tiviakov engine.
1.
e4
d5
2.
exd5
Qxd5
3.
Nc3
Qd8
4.
d4
Bf5
5.
Qf3
Qc8
6.
Bf4
7.
Nge2
еб
8.
g4
Bxc2
9.
d5
Bg6
10.
dxe6
fxe6
11.
Bh3
Nf6
12.
g5
Nd5
13.
0-0
Be7
14.
Nxd5
cxd5
15.
Nd4
Bf7
16.
Rfe1
0-0
17.
Nxe6
Qc6
18.
Rac1
Qb6
g
h
19.
Nxf8
Bxf8
20.
Rc8
Nc6
21.
Rxa8
Nd4
22.
Qa3
Nf3+
23.
Kh1
h5
24.
Qxf8+
Kh7
What should I play against 4.Nb5 in the Qd6 Scandianavian? I checked games explorler but only see 1 game. Black won the game but he had a passive position for a while. Is 4.Nb5 a mistake from white?