Chess Opening Theory/1. e4/1...Nf6/2. e5/2...Nd5/3. d4/3...d6/4. Nf3/4...dxe5/5. Nxe5

White retakes the pawn with their knight. e5 is a good square for this knight. It exerts crushing control over the light squares. With inaccurate play Black can easily go wrong, (e.g. 5...g6 6. Bc4 Nb6?? 7. Bxf7#). Therefore, Black would like to dislodge this troublesome knight and greatly free their position. How are they to do so?

Black cannot kick it away yet. 5...f6? 6. Qh5+! g6 7. Nxg6 hxg6 8. Qxh8 +-. They cannot trade it away yet either. 5. Nc6? or 5. Nd7?, thinking to trade off the knight, is too costly. One line is 5...Nd7? 6. Nxf7 Kxf7 7. Qh5+, with a double attack on Black's knight on d5. 7...g6 8. Qxd5 +-.

The main line is 5...c6. This defends the knight on d5, therefore prepares ...Nd7 to smoke out White's knight by nullifying the danger of Nxf7 Kxf7 Qh5+.

There's little White can do to prevent ...Nd7. 6. c4?! is inaccurate because of 6...Nb4!: this move now works because the pawn on c6 also prevents Qh4 from coming with check. There is a trap here: 6. c4 Nb4 7. a3? Qxd4!. If 8. Qxd4 Nc2+ forks the king and queen. 8. axb4 Qxe5+ and Black is up a pawn. The main line continues 6. Be2 Bf5 7. O-O Nd7 8. Nf3 e6 ⩲.

5...g6 is playable. Black usually answers 6. Bc4 with 6...c6 to defend the knight anyway. 6...Bg7 7. Nxf7 Kxf7 8. Qf3+ Ke8 9. Bxd5, Black loses castling rights and a pawn, which Black can get back 9...Rf8 10. Qb3 c6 11. Bf3 Qxd4 ⩲.