The Declined, 5...Nb4 is a variation of the Belgrade Gambit, catalogued as ECO C47. The line runs 1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. d4 exd4 5. Nd5 Nb4, reaching the position shown below after 10 half-moves.
Both sides have pawns in the centre (White on e4, Black on d4). Development is level at two minor pieces each, and Black is up a pawn of material. It is White to move after five moves. Black has doubled pawns on the d-file.
On the Belgrade Gambit generally: A gambit in the Four Knights where White plays Nd5 instead of recapturing the d4 pawn. Creates immediate complications.
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See all 5 Belgrade Gambit variations →
The Declined, 5...Nb4 goes 1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. d4 exd4 5. Nd5 Nb4. It is a variation of the Belgrade Gambit and is catalogued as ECO C47.
The Declined, 5...Nb4 is ECO C47. ECO codes group openings by their move order, so nearby codes cover closely related lines of the Belgrade Gambit.
Stockfish evaluates the position after 1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. d4 exd4 5. Nd5 Nb4 at -0.31 at depth 18, which is a slight pull for Black, within normal opening margins. Engine evaluation is only a starting point — at club level the practical value of a line is mostly about whether you know its plans better than your opponent does.
Both sides have pawns in the centre (White on e4, Black on d4). Development is level at two minor pieces each, and Black is up a pawn of material. It is White to move. Black has doubled pawns on the d-file.