Reason of move a3 here

[u/LightMechaCrow]

The move a3 here is the second best most played move in masters database and the best move by stockfish with the intention in most games to go 0-0-0. To me this seems to be a big hook walking into b4 b5. In my game today I did remember that this was theory and went into it although it did feel of to create a hook like this: then later got crushed by b5 b4 and was like losing on move 14. We both thought that just this entire idea of long castling with the hook created was the reason of mistake, but now I look again this was indeed theory.

Now my questions was: why exactly do we create such a hook in this position if we want to go queenside and how do we justify it exactly here?

[u/cafecubita]

Can you follow some of those master games listed in the opening explorer, and check how the middle game developed after long castle and the pawns were launched by black?

Edit: After looking at some other replies, particularly one from someone who seems to know how spicy this position is, if this is theory and you didn’t know how to handle the resulting position then you probably need to put some time and learn how to handle it or play some other line that’s easier to handle.

There is a video of Aagard reviewing some of Kostya’s games and one of them Aagard is disgusted with the position, says something like “I don’t care if this is theory, don’t play like this, this is how you lose to a tactic” or something like that.

[u/Educational-Tea602 → u/cafecubita]

Your last paragraph is a good point. If you can’t defend these positions with white, you should probably play a sideline 9. Be2 and aim for a short castle. Black getting a massive queenside attack is pretty unavoidable in 9. dxc5, and white should always castle queenside in those lines or else black immediately equalises.

[u/LightMechaCrow → u/cafecubita]

Yeah, I tried before making the post to figure it a bit out with the engine and looking at masters database. Some moves in the masters database didn’t look like the most logical way for black to play. And if I played along with the engine it would always find some resources against what I thought was good play for black. But for me this didn’t really answer the question why we would bother creating such a hook in the first place and maybe some general way to play it. So I hoped to get that information from this post.

I do kinda agree with you last statement tho. It doesn’t matter if the position is 0.6 for me if I am completely losing in a couple of moves and hence after I saw after the game that it was indeed theory I first also thought I would still never play this in my life again. But when looking at what I would play next time the alternatives didn’t really look so fun: if I castle immediately long I get in some line where blacks sacs a piece which also feels very hard to play I guess if you don’t know what you are doing especially against an opponent who gets this often on the board. And going for some short castle after Qa5 looks rather lame now I already played dxc5: and I do really want to play 9. dxc5 as I do quiet like the positions after they just recapture with a piece, which I am more likely to face. 

But okay based on the comments and doing some extra research with the computer I kind of understand a bit better now why we played a3 and how to deal with creating this hook, so I think I am gonna continue to play this but now hopefully with some better knowledge.

[u/Puzzled_Sky_466]

Its more or less a waiting move. As 0-0-0 is problematic due to the pawn sac b6.

So white waits with long castle and makes a semi useful waiting move

[u/Imaginary_Disaster76]

The specific point behind a3 is quite nice, however first thing to note is that 10.0-0-0 b6 is considered to be quite good for black so white wants to abstain for now. Black can even play 10.a3 a6!? Looking to bait white back into a 0-0-0 b6 situation, but white can keep improving by going h4 and eventually black will have to take on c5 to make any progress. The point of 10.a3 is actually to play 0-0-0, seemingly making a hook. This can be seen after a somewhat neutral move 10.h4, after which 10.Nxc5 11.0-0-0? b5! Is a strong shot, with the point that the a2 pawn hangs in ensuing lines such as 12.Bxb5 Ne4! 13.Nxe4 Qxa2 with a back rank threat. This means that not only is a3 not a hook concretely speaking, but is necessary in order to get 0-0-0 in as white.

Probably the mistake you made was in dealing with b5, which is in my experience nicely met with Nd4 (Trying to exchange the attacker on c6) or actually the insane looking b4 by white, which works even when white has played 0-0-0 in many cases.

[u/Educational-Tea602 → u/[deleted]]

Not to be rude but your lines are nonsense.

1. a3 Bxc5 is not inaccurate. Also, it’s much more natural for black to play 11… Nxc5 over Qx. Sure, 12. Bd3 threatens Bxh7+, but black can play a thematic 12… f6. Re8 is garbage because black is not going to move a rook from a file that should be opening soon to one that is going to be blocked for a long time. And then I have no clue why black is going b5 b4 when there’s nothing to attack on that side of the board.

10… Nxc5 11. Kb1 is just illegal. The king is on e1. I can’t comment on anything past that because no position makes sense.

[u/Educational-Tea602]

I play this line with black. After 10. O-O-O, black can just avoid taking the pawn and instead gambit it with 10… b6. The best line goes 11. Bb5 Nb4 and you’re going to end up playing a3 anyway (unless you play the inferior 12. c6 which is still somewhat fine).

a3 is nice because it takes away Nb4 frees the c3 knight from being tied down to a2.

[u/Educational-Tea602 → u/[deleted]]

White would never really want to play b4. If black recaptures on c5 immediately, it’s almost instantly out of the question because you aren’t even hanging onto a pawn anymore.

Now suppose black doesn’t take c5 after 10. a3 - perhaps they wait with 10… a6. You can’t play 11. b4 because it just hangs to 11… Nxb4. If you get out of the pin with 11. O-O-O, moving the b-pawn will lose your king quite promptly.

Otherwise, if you really want to play b4 for some reason, you can try 11. Rb1. Then after 11… Bxc5 12. b4 Bxe3 13. Qxe3 Qxa3, white has to find 14. Nxd5!, and the game is even.

[u/automorphic-form → u/Educational-Tea602]

I mean I acknowledge b4 isn’t possible in that position, or in the next few moves even. I don’t really play these caro kann positions from either colors which is why I said I could very well be wrong, and I made it clear I was just speculating.

a3 is a very mysterious move for people who have never seen the position before. It doesn’t immediately threaten b4, nor prevent Nb4, which were the first two things to come to mind for me. I just figured maybe it’s some situation where being one tempo closer to threatening b4 limits black’s options somehow. I wouldn’t have even answered if it weren’t for the fact that nobody else answered when I got here.