Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nf6/3. Nxe5/3...Nc6/4. Nxc6/4...dxc6/5. f3

5. f3 defends e4 and prevents Black's knight from coming to g4. White therefore achieves their first two priorities in refuting the Stafford gambit in one move.

5. f3 looks very unnatural because conventional wisdom is that moves like f3 or f6 weaken the kingside. However in this situation it is surprisingly sound, and a straight-forward way to refute the Stafford gambit.

If Black plays 5...Bc5?!, the usual Stafford move, White delays developing pieces still further and continues with 6. c3 O-O 7. d4 Bb5. White gets a huge centre and plenty of safe space to develop which Black, having removed their pawns from the centre, cannot contest. 8. a4 threatens to trap the bishop.

Black, knowing that the f-pawn is usually a poor defender of the e-pawn, may assume this 5. f3 is the Damiano defence with colours-reversed, and snap of the e-pawn with 5...Nxe4?.

However, because Black has no e-pawn, this does not work out: 6. fxe4 Qh4+ 7. g3 Qxe4+ 8. Qe2 and Qxh1 isn't possible because Black's queen is pinned to their king. 9...Qxe2+ 9. Bxe2 and White gets an endgame where they are up a minor piece for a pawn.

Thus the engine recommendation for Black is 5...Be6: interposing on the e file to prevent the eventual pin and reinvigorating the threat of Nxe4. 6. Qe2 is White's strongest reply: defending the e pawn but keeping the idea of c3 and d4 possible.

5...Nh5 is Black's trickiest reply. The idea is to support the threat of Qh4: after (e.g.) 6. Nc3? Qh4+! 7. g3 the knight can take on g3. 7...Nxg3 8. hxg3 Qxh1-+. The most straightforward way to defuse this threat is 6. g3, preventing the queen from coming to the h4 square in the first place.

For explanation of theory tables, see theory table and for notation, see algebraic notation.

1. e4 e5 2. Nf3 Nf6 3. Nxe5 Nc6 4. Nxc6 dxc6 5. f3

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• Youtube: Refuting unsound Gambits | Stafford Gambit - Andras Toth