This line is easy to learn, very effective and almost nobody knows it.
The chess variation Qf6-Defence is part of the Classical or Cordel Variation. It is very seldom played among grandmasters. The reason is probably a general dislike to bring the Queen out early in the game.
I tested this variation and like it very much. I find that if White trys to win by force he often runs into a bad position himself and loses.
I tell you a secret. This move is an idea of the Fritz chess program, so Qf6 can't be a bad move. I played a lot of games in the internet with this opening but couldn't find a refutation. There is one uncomfortable variation, but when you know how to handle it you should be right.( Study the piece sacrifice in Game 2 move number 9 )
The critical line which is most uncomfortable for Black because White does not castle right away but saves time and plays 5.d4 right away (instead of 5.0-0).
1.e4 e5 2.Nf3 Nc6 3.Bb5 Bc5 4.c3 Qf6 5.d4 exd4 6.e5 Qe6 7.cxd4 Nxd4!? 8.Nxd4 Qb6 9.Be3 Bxd4 10.Bxd4?! (even better seems to be 10. Qxd4! Qxb5 11.Nc3, I wouldn't like to have Black here...) The point is when White castles early before he plays d4 then you have more time and can play Ne7 developing another piece. (example: 5.0-0 Nge7)
Don't worry! Almost nobody will find this unpleasant line in a real game, many castle and play d4 later. But we can improve on it for Black and play the improved line below.
So don't play 7...Nxd4? but 7...Bb4+ 8.Nc3 Nge7 9.0-0 d5 10.Bd3 Ba5 (not 10...0-0 because of Bxh7+) 11.Ne2 f6 12.Nf4 Qf7 13.exf Qxf. This chess variation is still a bit better for White but Black can survive I think ....
Memorize this line just in case that White finds and plays the uncomfortable line 1.e4 e5 2.Nf3 Nc6 3.Bb5 Bc5 4.c3 Qf6 5.d4!. If he doesn't find it then you probably win with a crushing attack at the kingside.
|Basic position with c3 - White to move -|
I call this the slow setup as White has played a pawn move (c3) and not a piece move (Nc3). This allows you to make the protecting pawn move h6, after White has played d3, to protect your queen from Bg5.
|Basic position with Nc3 - White to move -|
I call this the fast setup because White has developed the knight to c3 and not played c3 (a pawn move).
White will play now d3. In this fast setup (Nc3) you should not play h6 to stop the bishop from attacking your Queen, but the queen goes to d6 instead when attacked by Bg5 (Qd6).
The idea behind this is that White has developed a piece (Nc3) and has not played a pawn move (c3), which is slow. So you should develop a piece also, and not make a pawn move (h6) after d3, which is losing valuable development time. So after White has played d3, you castle which is equivalent to a piece move.
Qf6 Variation - Fast Setup