Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...a6/4. Ba4/4...Nf6/5. O-O/5...Nxe4

Black takes the free pawn. However, while Black's king remains in the centre, they must navigate the danger of an open e-file carefully, and White can eventually recover the e-pawn.

How is White to recover the pawn?

6. d4 is the main line. White controls c5 (preventing ...Nc5) and threatens Black's e5 pawn. If Black takes it 6...exd4?!, the Riga variation, they run into complications from Re1 due to opening their e-file with their knight and king still on it. Therefore the continuation is usually 6...b5 7. Bb3 d5, and White gets the pawn back 8. dxe5.

The natural 6. Re1?!, intending 6...Nf6 7. Nxe5, is in fact a very minor sideline. Black's knight can retreat to c5 instead, hitting the bishop and forcing White to trade it for the c6 knight. After 6...Nc5 7. Bxc6 dxc6, Black is doing well compared to the exchange variation (with 4. Bxc6): White lost a tempo moving the bishop to a4 then back to c6, and the disappearance of the centre pawns favours Black's bishop pair.

Likewise, now that Black's rejoinder ...Qd4 wouldn't come with a fork, White may want to try 6. Bxc6?! first. 6...dxc6 7. Re1 (to expel Black's knight, or 7. d3) Nd6 8. Nxe5⩱. White avoids the more theoretical main lines, but Black is equal or a little better and is afforded easy development. It's not necessary for White to give up the bishop pair to recover the pawn if they follow the main line instead.

The open defence is one of the most direct and combative ways for Black to meet the Spanish game. It is employed at all levels of the game.

The earliest recorded game in the open defence was played by Robert Brien and Robert Wormald (in consultation, with the black pieces) against Johann Löwenthal (1810―1876) in 1854. Löwenthal played a line beginning 6. Re1 and triumphed after a flashy queen sacrifice. His play was described by chess wit William Napier as "like a man enraged, [he] smites his enemies hip and thigh."^[1][2]

Among its highest level appearances, it was the defence chosen by Viktor Korchnoi to meet Karpov's 1. e4 in the 1978 and 1981 World Championship matches.

1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. O-O Nxe4

• Mikhalevski, Victor (2013). The Open Spanish. Glasgow: Quality Chess. ISBN 9781907982446.
• Flear, Glenn (2000). Open Ruy Lopez. London: Everyman Publishers. ISBN 185744261X.

Wikipedia has related information at Ruy Lopez.