Four Knights Game

The position is now completely symmetrical, leading to a somewhat drawish position.

There are a range of moves played here, but by far the main tries are 4. Bb5, developing the bishop and pressuring the centre, and 4. d4, opening the centre and transposing into a variation of the Scotch game.

With both knights developed, next on White's list is to develop their king's bishop, after which they will be ready to castle.

The prime position 4. Bb5, called the Spanish variation, is the main move. As in the conventional Spanish game or Ruy Lopez, the bishop on Bb5 indirectly pressures Black's centre by threatening to trade off the knight guarding e5. There are key differences from the normal Spanish game: White does not have their usual plan of c3 and d4, because the knight is on c3, and their e4 pawn is defended so 4...a6?! Bxc6 dxc6 Nxe5 plays out differently. The two main lines are 4...Bb4 and 4...Nd4.

Where else might the bishop go?

4. Bc4!?, called the Italian variation, allows 4...Nxe4! and a centre fork trick. White can navigate it without losing material, 5. Nxe4 d5 6. Bd3 dxe4 7. Bxe4=, but allows Black a free hand and control of the centre behind e5. Essentially unheard of in tournament play, 4. Bc4 is nevertheless the most common amateur move.

4. g3, the Glek system, prepares to fianchetto the bishop to Bg2, castle, and play d3, in the manner of the King's Indian attack. The Glek is a modern treatment of the opening and is less drawish than the other four knights games.

4. d4 is the Scotch variation. This is a forthright approach, White wants to remove Black's pawn from e5, half-open the centre, and have space and open lines by which they can develop their pieces. This resembles the Scotch game (1. e4 e5 2. Nf3 Nc6 3. d4) and the game may transpose to the Schmidt variation of the Scotch after 4...exd4 5. Nxd4 Bb4 6. Nxc6 bxc6 7. Bd3. In the four knights Scotch, however, White also has the option of 5. Nd5!?, the sharp Belgrade gambit, which often hopes to ensnare Black after 5...Nxe5 6. Qe2.

4. Nxe5?! is the Halloween gambit. White gives up a knight for a pawn, then takes space in the centre and a development lead by nudging Black to undevelop. Objectively dubious, it is nevertheless intriguing and offers White many aggressive and practical chances, especially in faster time controls.

4. Nd5!? was a blitz favourite of Daniel Naroditsky. This undefends the e4 pawn. After 4...Nxe4 5. d4 exd4 6. Bd3 Nc5 7. O-O= White is down two pawns but has compensation and an active position.

Two interesting "waiting moves" serve to pass the turn back to Black. Due to the symmetry of the position, this usually leads to something resembling a normal four knights game but with colours reversed.

4. a3!? is the Gunsberg variation, a useful waiting move that prevents 4...Bb4.

Black should avoid 4...Bc4?! on account of 5. Nxe5 Nxe5 6. d4 Bd6 7. f4! Nc6 8. e5. Black can put the bishop on d6 instead, but wouldn't want to do so if it means trapping their d-pawn at home. So, 4...d5 is the best move, and the position resembles a four knights Scotch in reverse. 5. exd5 Nxd5 6. Bb5 Nxc3 7. bxc3 Bd6 8. d4 exd4 9. cxd4 O-O 10. O-O=.

4. h3!? is a trendy line popularised by Anish Giri. It prevents the possibility of a ...Bg4 pin in the future but otherwise just passes the turn to Black. The position is sort of a four knights with colours reversed: Black's main moves naturally enough are ...Bb4 and ...d5.

Known since the 16th century, the four knights became popular after the Romantic era as the chess world moved on to the positional style of chess. It had its heyday in the early 20th century, and was reinvigorated in the 1990s.^[1]

1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6

Wikipedia has related information at Four Knights Game.