Why would a GM choose this line?

For a lowly club player like me, I've looked at these lines and decided black's play is too straightforward, and white is the one who has to be accurate. For GMs I assume this is just a less ambitious way to go for a draw with white? (and Hammer's 16.Nf5 was just an unfortunate blunder)

Instead, why not:

I've decided the "trick" to these positions is you're getting a Spanish Breyer (...Nd7 was one move instead of 3, Bc2 will be 3 moves instead of 4 and white is playing without h3 so it evens out) but the point is that c5 is early and especially if b5 is played this is a somewhat well known structural error in the Breyer (black usually waits for white to play a4 before playing c5 so that b3 is no longer supported by a2 when a black pawn appears on c4)

Also, of course, as a Spanish player I don't mind making my 1...c5 opponent play a breyer

Oh, but here's a move order

It's an ambitious way to drag your opponent out of GM opening preparation, a thing which me, you and 15 million chess.com members are too immortals to understand.

I believe Hammer wanted to play some ( usual to him ) unusual idea, only that sometimes, this project is enough to trick the innovator himself. So be it, the transposition from a Canal Sokolsky to a Hammers Chekhover didn't work. How all this are related with the "Sicilian Breyer " functionality it's perhaps something the OP needs to answer himself too because the example doesn't match the occasion...me say.

Nevermind...we live in a free world.

Yeah, I sort of answered it myself right away  Sometimes posting helps me organize my thoughts.

Most importantly, I missed it's not going to be a Spanish without ...e5 on the board, so black has many options. I do think this will be a good way to outplay some of my peers though because there are a few pawn structure nuances related to the Spanish that I'm not sure a Sicilian player will be aware of (if they're near my level).

As for "prep" (I guess you mean theory? amateurs don't face prep) one of my favorite things to do OTB is play a few non book moves on purpose to screw with my opponent.

If you do mean theory, you have to consider this line of Hammer's is well known (even to a player like me) and Svidler plays it perfectly here... so to my eyes it's just an unambitious try that backfired. Getting a board full of pieces, especially if you get a Spanish position, is a much better try to outplay your opponent, IMO.

So... his choice doesn't make sense to me... did he have an idea in this line we didn't get to see? Was he going for a draw? Did he expect Svidler to not know this line? The most obvious answer is my understanding of chess (and choices like this) is extremely far below Hammer's  

No, theory and preparation are two different things. Perhaps preparation depends on theory but that not makes it an absolute " go together ". There are dozens the examples where GM's drive away from best theoretical lines to a positional inferior home preparation, for various reasons. 

Hammer is a well known Canal Sokolsky player where likes to do many things to transpose opening ideas. If you check his games with White pieces against the d6 Sicilians you will understand. If you check his games, in general, you will understand more...

That theory and prep are different was my point to you after you criticized amateurs regarding prep 

But yeah, I don't know Hammer other than he's a GM from Norway. I haven't looked at his games at all.

I also play the Rossolimo. I wonder what sort of transposition he could have been trying here.

Now that you mention it, it actually looks like Hammer was the confused one after Svidler didn't play 8...h6 but instead chose 8...Rc8 with 9...Be6. Svidler's play seems super efficient, and on move 14 as white I'd have no idea where my play is supposed to be coming from.

Ok, Hammer is a GM, he doesn't get confused like I do... but his move 16.Nf5 seems to indicate he really wasn't sure how to continue.

No, i didn't criticize amateurs about preparation. I said that we non-professionals do not understand the importance play chess out of the comfort zone of your opponents and preparation. A 80% of experts-advanced players rely on to play their opening ideas depending on theory-homework and independent what the opponent's history suggests.

In the other level of chess professionalism...things are quite different.

I normally have enough decades of experience to put my 2 cents in about the ideas behind various openings. But the Rossolimo or Canal Variation just stumps me as to any logic.  If Black plays 3...Bd7 then 4 Bxd7 Q/Nxd7 and Black has one Piece and two Pawns developed and White only has one Piece and one Pawn - effectively handing over the advantage of the first move to Black.

Sure enough, chess.com's Opening Explorer shows 29% wins for White, 42% draws, and 29% wins for Black in master games after 4...Nxd7.  Moves that challenge the center like 5 Nc3 or 5 d4 or 5 c4 have disastrous avg. results for White, who is forced into the sort of passive opening Black usually experiences.  The latest Stockfish development engine, 181117 (18th of Nov. 2017) with 20-ply analysis says White is +0.19P with 4...Nxd7 and +0.22P with 4...Qxd7.  After the next two very most common moves after 4...Qxd7, 5 O-O Nc6, White is up +0.07P.  After the next two very most common moves after 4...Nxd7, 5 O-O Nc6, White is up +0.28P.

I don't see any compensation in something that's going to lead me to a strong, playable middlegame for throwing away two tempos to one when trading Bishops.

I did try it once, in a team game against a former Sydney, Australia high-school champ and, of course, it ended in a draw:

It's just that, usually my opponents don't have a history (not one that I can look up).

Maybe it's different in Europe where your opponents might be in something like chessbase. In the USA I will only see games in chessbase if my opponent played in a FIDE rated event, and even then they're not always there.

This leads to some funny things... one guy told me whenever he playes in a FIDE event he doesn't use his usual openings. That way it's harder for people to research him.

Also pro prep is different because they're facing the same dozen (or so) guys year after year, and can even know their pairings months in advance. In a club swiss I might not know my pairing until 5 minutes before the game starts.

I'm not ignoring you, but I don't have time to read a lot right now, I'll come back to this, thanks

I play both. I find compensation in the fact that black isn't going to get the dynamic, open Sicilian type of game that most of them are aiming for. We all know Sicilian junkies spend a bunch of time on their najdorfs, dragons and so forth. How many of them take the time to study "boring" positional struggles that come from the Moscow and rossolimo? Not that many in my experience. I know a decent amount of theory. When I used to give black an open Sicilian, most of my opponents ( regardless of rating) would blitz out tons of book moves without thinking at all. Now I get to sit back and chuckle when I play 4.c4 in the Moscow 3...Bd7 lines and my opponents start burning clock because they don't know what to do on move 4.

5.Bd3 would hardly be a suprise to Svidler, as it was played against him by a random chessplayer named Magnus Carlsen.

Hammer's 9.Nd2 is thematic, but slow in that position. Either 9.0-0 or 9.Bg5 are more pressing moves, IMO.

Of course 5.Bd3 would not surprise any GM (and even if it did, they would soon understand what was going on I'm sure). My patzer-ish impression was Hammer's line is drawish, and I was wondering if Hammer was earnestly playing for a win against Svidler in that game.

Instead of wondering tell me what you see? Is this a picture of a player who has popularized a certain opening idea? I think it is. How a GM at this level anticipate the competition when his repertoire is narrowed to a specific line?

The witness and conclusions is yours.

It seems in the Hammer -Svidler game, white got into trouble when he gave up the center without much resistance.

In my experience, with the Bb5 ... Nd7 line, white can bring the B back, holds the center, and tries to weather black queen side expansion. Basically hoping for over extension and slight lack of development.

Or can exchange the B on d7 but then really has to try to hold the center with some sort of Maroczy Bind structure or with Nc3 and pieces.

It appears in most or all of the other Hammer games shown, he generally follows those ideas.

I doubt he could popularize the Moscow (3.Bb5+ whatever people call it these days) with results like that lol 

From the games you show, out of 6 whites he won once, and it was against a player rated 300 below him.

I guess you're his fan and think very highly of him?

Well if we're evaluating using beginner stuff, we can say that after the light square bishops are traded black has pawns on dark squares and white has pawns on light squares, so white's minor pieces are better (good vs bad bishop unless black spends more time moving his pawns off those squares).

Anyway, you can often get Maroczys which are comfortable for white and torturous for black, although I suppose it's just a matter of knowing how to play the positions, the statistics mean very little in this regard. Get to move 10 or 15 and suddenly the stats are 70% for white if you know the right move.

Besides, I'm not about to make my tournament games a test of who knows more theory, that's really boring to me, so I don't go into mainline Najdorfs for example. Especially against all these kids who know nothing about chess. Get them in a strategic game and they completely collapse.

That's when they recapture with a queen. When they recapture with the knight you can get other easy to play positions. For example

Can you translate this to English, please?

 I guess you are intentionally missing the point to excuse your operation creating this thread. If this is about after all...i have nothing more to add. 

Your Honor? may the Jury be instructed to disregard my observation-interfere?

Thank you.

Honestly I have trouble understanding each of your posts, I think there is some language barrier between us. I'm not doing it intentionally.

Similarly I think you've misunderstood my first post in this thread.

I guess you're saying Svilder was able to prepare because Hammer is well known to choose this line. Maybe you're also suggesting that Hammer plays this line often, so it must mean that he doesn't only play it for a draw.

Still, I see it as an unambitious try, and his results (and frankly the reputation of the line itself) seem to bear that out.