Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...Qf6/4. d4

=Ruy Lopez - 4_d4!?=

The move 4. d4 is an aggressive and risky response to black's move, after Black plays 3...Qf6, a sideline. The idea is to sacrifice a pawn for a strong attack on the black king and the center. The move 4. d4 has the following pros and cons:

Advantages:

 * 1) It opens up the center and creates more space for White's pieces.
 * 2) It threatens to win the black e-pawn with 5.dxe5 or 5.Nxe5, or to fork the black queen and knight with 5.Nd5.
 * 3) It prepares to bring the knight or the bishop to the d-file, creating more threats and possibilities for tactics.

Disadvantages:

 * 1) While White attacks the bishop on c5, the line 4...exd4 5. Nxd4 Bb6, where Black's bishop goes on a more active square or, exchange with 5...Bxd4. Black can capture the pawn with 4...exd4, and White has to prove that they have enough compensation to stop the strong bishop on b6.
 * 2) It exposes the white king to a possible attack by the black queen on h4, especially after White castles short. Black can also play g5 to prevent White from playing Bg5 or Ng5.
 * 3) Other than capturing, It allows Black to play 4...d6, defending the e5-pawn more and preparing to play Be7 followed by O-O, with a solid and safe position.

The move 4. d4 is a very sharp and complex move, which requires a lot of calculation and accuracy from both sides. It can lead to many different variations.

Continuations:

 * 1) The Cordel Gambit: 4...exd4 5.O-O Ne5 6.Nxe5 Qxe5 7.c3 Bc5 8.cxd4 Bxd4 9.Nc3
 * 2) The Schlechter Variation: 4...exd4 5.O-O Bc5 6.e5 Qg6 7.Bxc6 dxc6 8.Nxd4 Ne7
 * 3) The Alapin Variation: 4...exd4 5.e5 Qe6 6.O-O Bc5 7.Bxc6 dxc6 8.Nxd4 Qd5
 * 4) The Leonhardt Variation: 4...exd4 5.e5 Qg6 6.O-O Bc5 7.c3 dxc3 8.Nxc3 Nge7