Chess Opening Theory/1. e4/1...e5/2. Nf3/2...f5/3. Nxe5

White is threatening the fearsome Qh5+, which, supported by the knight on e5, can't be successfully defended by ...g6. There's also the incidental threat of exf5.

So that's the Latvian gambit refuted then? Most top players would say "yes". But there is a particularly optimistic breed of chess player that looks at the pawns on f5 and e4 and thinks that if the knight could just be driven away from e5, it's Black who will be capturing a pawn (fxe4), and possibly even defending it with ...d5.

And so the move 3...Qf6 was invented. Yes, it's not usual to move the queen so early, but then again, following up a wild lunge like 2...f5 with solid-looking moves is a recipe for disaster.

3...Nf6!?, which controls the h5 square, may also be tried. White can offer back the pawn with 4. Bc4, not least because 4...Nxe4?? gives up control of the h5 again. To prevent Bf7+, driving the king to e7, Black may try 5. d5 exd5 Bd6 6. d4 O-O 7. O-O Nbd7± or 5. Qe7 to give the king luft on d8.

3...Nc6? is the Fraser variation: "You're threatening to win the exchange? Coward! I shall FORCE you to win the exchange!" Black encourages 4. Qh5+, intending to gain time on White's queen to leverage into an (unsound) attack. Unfortunately for Black the moves to defuse the attack are pretty natural. 4. Qh5+ g6 5. Nxg6 Nf6 (attacks Queen, defends h7) 6. Qh4 Rg8 7. Nxf8 Rg4 8. Qh3 Rxe4+ 9. Be2 Qe7 10. Nc3 Rxe2+ 11. Nxe2 Nd4 12. Qd3 Nxe2 13. Qxe2 Qxe2+ 14. Kxe2 Kxf8+-, White is up more than an exchange in the endgame.

1. e4 e5 2. Nf3 f5 3. Nxe5

Wikipedia has related information at Latvian Gambit.