Classical Variation, Greco Gambit, Traditional Line

After 4...Nf6 5. d4 exd4, the recapture 6. cxd4 gives White two center pawns abreast on d4 and e4. The d4-pawn attacks the bishop on c5, and the position belongs to the Center Attack, the old main line of the Classical Variation. The engine judges it level, but only if Black responds with energy. Leaving White's center intact gives White space and a free hand.

The usual reply, chosen in roughly three games out of four, is the check 6...Bb4+. It gains time against the center and leads to the gambit lines with 7. Nc3 Nxe4 8. O-O, including the Greco Variation (8...Nxc3) and the Main Line (8...Bxc3). White can also block more quietly with 7. Bd2 or 7. Nbd2. The retreat 6...Bb6 is the main alternative and is much less ambitious. It concedes the full center, and White scores noticeably better there. The engine also rates the immediate counterblow 6...d5 highly. Taking the pawn with 6...Nxd4 is rare and gives White good results in practice.