In this variation of the Modern Defense, White takes advantage of Black's constricted position and the vulnerability of the f7 pawn.
1. e4, g6
2. d4, Bg7
3. Nf3, d6
4. Bc4, Nd7??
The losing move. White jumps quickly on the vulnerable f7 pawn.
5. Bxf7 ....
5. .... Kxf7
Black captures the Bishop on what seems to be a correct reply. But it would be wiser not to take the offer: 5....Kf8, 6. Ng5 Nb6, 7. Qf3, f6 and White's attack would slowly fizzle out.
6. Ng5+!! ....
The timebomb! The King cannot retreat to e8 or f8 because of the threat 7. Ne6. The King has no choice but to come forward and surrender.
6. .... Kf6
7. Qf3+ mate
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