Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...a6/4. Ba4/4...Bd6

Morphy defence Spanish opening → Morphy defence → 4. Ba4 4...Bd6!? Black over-defends their e-pawn with their bishop. This is an unusual place to put the bishop, because Black would have to move it again before their can play ...d6. Perhaps Black was thinking of chasing down White's bishop, as in the Norwegian variation, (4...b5 5. Bb3 Na5), but wanted to first relieve the knight of its duty defending e5 (in the regular Norwegian variation, Black is happy to answer 6. Nxe5 with ...Qg5 and recover the pawn that way). Perhaps Black just wanted to develop their kingside and castle as soon as possible, but if so ...Be7 (and the Closed Spanish) is a better placement. 5. O-O is a sensible move for White, and by giving their rook access to the e-file they may soon be able to exploit the bishop's awkward placement. An example line is: 5. O-O Nf6 6. d4 exd4 7. e5!, where 7...Nxe5 8. Nxe5 Bxe5 9. Qe2 (the bishop and d7 pawn are both pinned) O-O 10. Qxe5 +++. White should avoid probably now avoid exchanging the knight, as 5. Bxc6?! dxc6 helps Black to eliminate the drawback of the trapped d-pawn, and the game transposes into the perfectly sensible king's bishop line of the exchange variation.