Chess Opening Theory/1. e4/1...e5/2. Qh5/2...Nc6/3. Bc4/3...g6/4. Qf3/4...f5

...f5 parries the threat of Qf7# by obstructing the queen's vision of the f7 square. It also attacks White's e-pawn, and if Black is able to remove it, they might be able to play d5 and take over the centre.

5. exf5?!, thinking to clear the obstruction, is inaccurate, ultimately because it gives up control of the d5 square.

Black can't play ...d5 straight away. If 5...d5?!, apparently with tempo on the bishop, then 6. fxg6! and Black doesn't have time to take the bishop because White's pawn now controls f7: 6...dxc4?? 7. Qf7#!.

Instead Black should prepare ...d5 with 5...Nd4 first. This is a double attack on White's queen and the c3 square (threatening ...Nxc3+, Black wins the rook by a fork). Then:

• 6. Qd1 to defend the c3 square is most natural, which allows 6...d5.
• 6. Qg3!? allows the fork but sets a trap. 6...Nc3+ 7. Kd1 Nxa1?? 8. Qxe5!+ Qe7 9. Qxh8+-.
• 6. Qd5?? threatens 7. Qf7# and Qxe5+. This is very common but strictly inferior, and 7...Qf6 deals with both threats.

5. Ne2 is White's best move: controlling d4 so preventing ...Nd4. Then the game may continue 5...Nf6 (threatening ...fxe4, as the knight will prevent vision of f7) 6. Nbc3 (defending e4) d6 7. exf5 Bxf5 8. d3= for an even game.

1. e4 e5 2. Qh5 Nc6 3. Bc4 g6 4. Qf3 f5

• A Completely Pointless Refutation of Four Move Checkmate, Jonathan Schrantz (Youtube).