411 REFERENCE · Wikibooks
Chess Opening Theory/1. e4/1...e5/2. Nf3/2...d6/3. d4/3...Nd7/4. Bc4/4...Ngf6/5. dxe5/5...Nxe5
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Hanham variation C41 Philidor defence → Hanham variation → 5. dxe5
5...Nxe5
By recapturing the pawn with the knight, Black prevents 6. Ng5: this is because Black's knight is gaining time on White's bishop.
6...Bb3? concedes the initiative and gives Black time to develop. After 7. Bg4 pinning the knight, White still cannot play Ng5.
Therefore White must trade knights, 6. Nxe5 dxe5. This is to White's advantage as they will be able to leverage the open d-file to win a pawn (7. Bxf7+).
Theory table
+56789Nxe5
dxe5Bxf7+
Kxf7Qxd8
Bb4+Qd2
Bxd2+Nxd2 +/-
References
See also