The Four Knights Variation of the Sicilian Defense begins with the moves:
1.e4 c5 2.Nf3 Nc6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6
There are at least two other systems in the Sicilian where all four knights are developed very quickly (the Classical and the Sveshnikov), but it’s this particular variation which is known in chess circles as the Sicilian Four Knights. (Just to confuse matters there are also Four Knights variations in both king’s pawn openings and the English Opening.)
Mainline Of The Four Knights Variation
The Sicilian Four Knights is another logical looking line for Black, who plans to develop his kingside quickly. Black aims to do without the move …a7-a6 and White’s most critical way to meet the Four Knights is by trying to take advantage of this fact with an early Ndb5.
I should also mention the move 5…Bb4, which is known as the Pin Variation. This line is sharp but not very popular. One possible variation is 6.e5 Nd5 7.Bd2 Nxc3 8.bxc3 Be7 9.Qg4! 0-0 10 Bh6 g6 11.h4! and White has a very quick attack.
Threatening Nd6+. White’s main alternative is 6.Nxc6
The move 6…d6 is a very important alternative, after which 7.Bf4 e5 8.Bg5 transposes into the main line Sveshnikov. Indeed, in practice the Sveshnikov is sometimes reached in this fashion.
In contrast, 6…d5? 7.exd5 exd5 8.Bf4 is very bad for Black, who has no good way to deal with the threat of Nc7+.
The main move. 7.Nd6+ looks attractive on first sight, but 7…Ke7 is actually fine for Black. It’s true that he has now lost the right to castle, but following 8.Nxc8+ Rxc8 9.Bd2 d5! Black is well ahead on development and may continue with …Rhe8 and …Kf8 to put his king in safety. Another try for White is 7.Bf4!?, which leads to a very sharp position after 7…Nxe4 8.Qf3 d5 9.0-0-0 Bxc3 10.Nc7+ Kf8 11.bxc3.
Now 7…Ba5? 8.Nd6+ is good for White, as after 8…Ke7 there is no threat to the knight so it can remain on its commanding d6 outpost.
WARNING: Black must not allow White to secure a knight on the d6 square.
Staking a claim for a share of the centre.
9.exd5 exd5 10.Bd3 0-0 11.0-0
This is unlike a normal Sicilian position in that Black has space and easy development for his pieces. On the other hand, it’s White who has the better pawn structure; Black’s isolated pawn on d5 may prove to be a weakness in the long run. White may also hope to exploit his bishop pair in a position which is quite open.
Theory: The main line is not theoretical at all, but those wishing to play the 7.Bf4 variation with either colour are well advised to learn their stuff!
The main line with 6…Bb4 has never been very popular as most Sicilian players are not looking to reach the type of position seen in the last diagram. I found just over 1,700 games with 6…Bb4 in Mega Database, with White scoring well with 60%.