Tactical Analysis of a Complex Rook Sacrifice

My friend Pyre recently played in a rapid tournament, and when we went over his games, we came across a very interesting and incredibly complex rook sacrifice.
The variation did not actually occur in the game, but it allowed for some fascinating tactical analysis.

In the position below the question is should Black sacrifice the rook on e3?

The key position. Should Black sacrifice the rook on e3?

This is a very interesting position because even though the sacrifice on e3 looks very strong, and makes intuitive sense, the variations are very long and too complex to calculate all the way through at this point.

In a previous blog I had already written about this kind of sacrifice: somewhere in the middle between a very "concrete" and straightforward sacrifice (like the classic bishop sacrifice on h7, where there are typically only very few variations to calculate with lots of "only" moves), and a purely long-term sacrifice like for example the various positional exchange sacrifices in the French and Sicilian openings.

Pyre and I discussed this position on Skype, using a screen share of my Chessbase window. We did not have enough time to discuss this game with the detail it deserves, so some of our conclusions were wrong or at least inaccurate. However, that in itself allowed for some interesting observations.

This position would have likely occurred shortly after the rook sacrifice. 

The links to a more comprehensive (and accurate...) analysis can be found at the end of this article.

After we were done with our analysis, I looked at the position again, and only after that second analysis I finally turned to my engine to verify the analysis that we had done up to this point. The screenshot shows DEEP FRITZ 13's analysis after 20. Kg1:

In the position shown above after 20. Kg1, DEEP FRITZ recommends these moves for Black after about 30 seconds 

There are basically 3-4 variations worth looking into:

a) 20. ... Nxb4 

b) 20. ... Qg4+

c) 20. ... Qg3+

d) 20. ... d4

It is interesting to note that there are a great number of transpositions between these variations. It's also worth noting that due to the large number of checks Black has in all these variations on h3/g3/g4/, the number of variations and positions to consider is enormous, and too much for an amateur player to handle with certainty.

For a full analysis please refer to the link at the bottom of this article, but the main ideas are these:

Nxb4: to pin the Nc3, and potentially swing the Rc8 over to the kingside via the now available c6-square

d4: to undermine White's already wobbly center even further, open the g1-a7 diagonal for the Bb8, and prepare Nd4 to exchange the White Nf3, the key defender of h2

Qg4+/Qg3+: to shuffle White's King around to the right square (g1 or h1, depending on the variation), and then follow up with Nxb4 or d4

Of course, the ramifications of these moves are impossible to evaluate with great certainty when deciding whether to sacrifice the rook.

Even when looking at the game together, Pyre and I missed or underestimated the following opportunities:

a) Ba7+: We completely missed the idea that Black in certain variations can play Ba7+. With the Black queen on h3 it's a pretty common mating pattern. What may have contributed to us overlooking this move initially is that we were so fixated on the long diagonal b8-h2 that it would not even occur to us to place the bishop elsewhere. On the other hand though, when a bishop is fianchettoed on b7, moves like Ba6 to switch diagonals always occur naturally to me.

b) Ng4: We spent too much time analyzing this idea, at the expense of other more effective moves. Considering that so many kingside attacks involve moves like Ng4, and that it's a very natural and "human" move to make, it's not surprising that we gave the move too much credit. 

c) Nxb4: A "computer" move that pins White's Nc3, and activates the Rc8

Conclusions:

1. Some - in fact a large number of - combinations and sacrifices are too complex to be evaluated with certainty. In such situations, following John Nunn's advice in his "Secrets of Practical Chess", a chess player should follow his instincts. If experience and gut feeling tell you the sacrifice is sound, you should proceed with it even if there is not enough time to work out every detail.

I know, however, from own experience that this is VERY difficult. In my own tournament games I frequently did not follow this advice, and usually regretted it later.

2.  When analyzing a very tactical position (let alone a strategic/positional one), it is very important to do it without the help of a chess engine first. Even if this leads to some wrong conclusions initially, it is vital that you exercise your ability to calculate accurately. This not only builds your tactical skill set, but also gives you the confidence to handle difficult tactical positions. I will expand on how to use chess engines effectively in another article soon.

Link to the game analyzed here:

NN - Pyre, Rapid 2015

Link to the same analysis in PDF format:

NN - Pyre, Rapid 2015