Scotch Variation Accepted

The capture 4...exd4 changes the problem compared with the Scotch Game proper. Because the knight already stands on c3, the pawn arriving on d4 attacks it, so White has no time for a leisurely recapture. White either takes back at once with 5. Nxd4, the choice in the overwhelming majority of games, or moves the threatened knight with 5. Nd5 or 5. Nb5. Engines rate the position as roughly balanced.

After 5. Nxd4 Black usually avoids 5...Nxd4?!, since 6. Qxd4 centralizes the white queen with no way for Black to gain time against it. Conversely, White welcomes the trade on c6, which comes with a hit on the black queen and saddles Black with doubled c-pawns. The main line is 5...Bb4 6. Nxc6 bxc6, recapturing toward the center and keeping queens on, whereas 6...dxc6 would allow their exchange. Play continues 7. Bd3 d5 8. exd5, when 8...cxd5 repairs the pawn structure, while the line catalogued as the main line runs 8...O-O 9. O-O, with both kings safe and Black relying on piece activity.

Black has several alternatives on move five. The modern 5...Bc5 is typically met by 6. Be3 Bb6 or by 6. Nxc6 bxc6 7. Bd3. The Schmid Defense, 5...Nxe4, offers the knight only temporarily: after 6. Nxe4 Qe7 7. f3 d5 Black regains material, and play may go 8. Bb5 Bd7 9. Bxc6 Bxc6 or 8. Nxc6 bxc6. The modest 5...d6 can lead into the Spanish Variation after 6. Bb5.

Of the knight retreats, 5. Nd5 is the Belgrade Gambit, which exists only through the Four Knights move order. White abandons the e-pawn, counting on a development lead and regaining at least one pawn later; Black's usual replies are the restrained 5...Be7 and the more demanding 5...Nb4. By contrast, 5. Nb5 is weak: 5...Bb4+ 6. Bd2 Nxe4 7. Bxb4 Nxb4 8. Nbxd4 O-O leaves Black a pawn up and castled, and Black scores well after it in practice. The counterattack 5. e5? fares no better, as 5...dxc3 6. exf6 Qxf6 7. bxc3 leaves Black with an extra pawn against White's doubled, isolated c-pawns.