Scotch Gambit

After 4. d4 exd4, White leaves the d4-pawn alone and castles, preferring 5. O-O to the more common 5. e5. The idea is to bring the rook to e1 quickly, where it supports the e-pawn's advance or pins a knight that captures on e4, while the pawn on e4 is offered to Black. The position also arises from the Scotch Game move order 3. d4 exd4 4. Bc4 Nf6 5. O-O, and some sources file it as the Classical Variation of the Two Knights Defense. The engine considers it roughly balanced, and White scores well in practice.

Black has four main replies. The most popular is 5...Nxe4, the Double Gambit Accepted, and White can answer 6. Re1 d5 7. Bxd5 Qxd5 8. Nc3, the Anderssen Attack, or try 6. Re1 d5 7. Nc3, the Canal Variation, or 6. Nc3, the Nakhmanson Gambit. 5...Bc5 leads to the Max Lange Attack after 6. e5, with very sharp play following 6...d5 7. exf6 dxc4 8. Re1+ Be6 9. fxg7. This is where White has the best results. The calmer choices are 5...Be7, the de Riviere Defense, and 5...d6, the Janowski Defense.