Chess Opening Theory/1. e4/1...e5/2. Nc3/2...Nf6/3. f4/3...d5/4. fxe5/4...Nxe4

=Vienna Game= Tension builds up. The Black knight begins to be threatening. White should react quickly.

A common mistake is to immediately take the black knight with /5. Nxe4/. After 5...dxe4, White has too few options to pursue his development; the f3-square is under control, the queen's bishop is blocked and the d-pawn cannot advance safely. Moreover, it is going to be hard to defend the e5-pawn against Nc6. It looks possible to catch up with 6. d4 but it seems that Black has equalized.

/5. Nf3/ looks like the most solid move. It defends the e5-pawn (who is quite fragile now that he is away from home) and secures the strategic d4-square. It also prevents the Qh4+ threat.

/5. d3/ is a good way to deal with the problem quickly. Black's knight will have to retreat or, more likely, to be traded with White's knight. White should be aware that Black can launch an aggressive attack with Bb4 and Qh4, sacrificing the knight, but preventing castling after 5...Bb4 6. dxe4 Qh4+ 7. Ke2 (7. g3 is bad because the white knight is pinned: 7...Qxe4+).

/5. Qf3/ is supposed to allow Nxe4 (or to force Black to play Nxc3) while playing an active game. But after 5...Nc6, things get complicated: 6. Nxe4 Nd4 and White must now defend the c2-pawn to avoid the fork (7. Qd3 dxe4 8. Qxe4 is a trap because of 8...Bf5).

Theory table
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1. e4 e5 2. Nc3 Nf6 3. f4 d5 4. fxe5 Nxe4