|The Four Knights Game is a chess opening starting with the moves|
1.e4 e5 2.Nf3 Nc6 3.Nc3 Nf6
although the knights do not need to be brought out in that order.
This opening is fairly popular with beginners who strictly adhere to the opening principle "develop knights before bishops". Usually the Four Knights leads to fairly quiet play but there are a few fairly sharp variations.
The usual move is 4.Bb5 which, if followed by 4...Bb4, leads to fairly symmetric positions; Black will typically achieve early equality and the game will end up drawn. However, Black can play more enterprisingly by 4...Nd4 (Rubinstein´s variation), which is, in fact, a
If White plays 4.d4 the Scotch Four Knights arises. This leads to more open games similar to the Scotch Game. This variation was played in the fifth game of the 1996 Deep Blue vs. Garry Kasparov match, and was the only game between the two where Black won.
A further possibility is 4.Bc4 (the Italian Four Knights). Black can either preserve the symmetry by 4...Bc5, or pseudo-sacrifice a knight: 4...Nxe4 (if 5.Nxe4, then 5...d5 regains the piece).
A dubious but dangerous gambit is the so called Halloween Gambit, 4.Nxe5?!. Black must accept the sacrifice with 4...Nxe5 and White will then take control of the centre with 5.d4 and proceed to chase the Black knights away, often back to their starting squares. Black must play carefully as he attempts to consolidate and make use of his extra piece.
Similar sacrifices from Black can arise if White plays the Glek Variation, 4.g3. Black can now make a Halloween type sacrifice with 4...Nxe4. This is probably more sound than White´s Halloween sacrifice since 4.g3 has weakened the important f3 square and robbed the g3 square from the White pieces. This line has been tried by Magnus Carlsen. After 5.Nxe4 d5 6.Nc3 d4, White entered a variation of the Vienna Game by returning the piece with 7.Bg2 rather than fight against prepared analysis.