Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...Nd4/4. Nxd4/4...exd4/5. Bc4

In this Birds defence sideline, White delays castling to move their bishop onto the a2-f7 diagonal. This renders Black's usual turn five options, 5...c6 or 5...Bc5, less effective. 5...c6 no longer comes with tempo, and 5...Bc5 runs into a serious trap.

After 5...Bc5? White can sacrifice the bishop on f7, then recover Black's bishop by forking it with their queen. After 6. Bxf7+ Kxf7 7. Qh5+ g6 8. Qxc5 (all forced) Nf6 9. Qxd4+-, White has won two pawns.

5...Nf6 is the main move. This develops the kingside and attacks e4. White's usual developing move to defend it, Nc3, is unavailable due to the enemy pawn on d4. It looks like White must waste time with a non-developing move to defend it, but they can actually 'gambit' it with 6. O-O, knowing they can recover it shortly. 6...Nxe4 7. Bxf7+ (7. Re1?! allows 7...d5 to secure the knight) Kxf7 8. Qh5+ g6 9. Qd5+ Kg7 10. Qxe4 and White recovers the pawn and trades a bishop for a knight.

5...c6 can be played anyway, but as it no longer comes with tempo it is less inviting. White can castle 6. O-O and it transposes to 5. O-O c6 6. Bc4.

For explanation of theory tables, see theory table and for notation, see algebraic notation.

1. e4 e5 2. Nf3 Nc6 3. Bb5 Nd4 4. Nxd4 exd4 5. Bc4

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Wikipedia has related information at Ruy Lopez

• Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.