Boden-Kieseritzky Gambit

The Boden-Kieseritzky Gambit arises after 2...Nf6 3. Nf3 Nxe4 4. Nc3, and can also be reached from the Petrov's Defense (Russian Game) or the Vienna. Instead of regaining e4, White offers to trade knights. After the critical 4...Nxc3 5. dxc3, the recapture frees the c1-bishop and creates the threat of Ng5 against f7, so Black has to cover e5 and stop the knight jump at once; 5...f6 is the only adequate reply. The scheme resembles the Stafford Gambit with colors reversed, but with the bishop already on c4 White is effectively a tempo ahead, which makes the attack safer.

The engine rates the gambit as not entirely sound, giving Black a slight edge, yet White scores well in practice and the line is popular at fast time controls. Black can decline with 4...Nc6, transposing to the Italian Variation of the Four Knights after 5. Nxe4 d5 6. Bd3 dxe4 7. Bxe4 with equality; White may instead keep the gambit with 5. O-O, when 5...Nxc3 6. dxc3 f6 joins the main line. Retreating with 4...Nf6 returns the pawn with a roughly level game, while 4...d5 is the Lichtenhein Defense.