Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Qf6

Black defends their e-pawn with their queen, but in doing so, Black prevents the natural development of their knight to f6, a critical square for knight activity in the opening. Conventional wisdom is against developing one's queen early: if it's attacked, then practically it must be moved, and this gives the opponent chances to develop with tempo.

This defence is rarely seen professionally as White is provided an advantage in development.

3. Nc3 develops a piece and threatens Nd5, with or without d4, to centralise the knight with tempo on the queen. This is a common move since black needs to play a prophylactic responce to White's threat, while that is happening the white pieces can keep developing with Bc4 and O-O.

3. Bc4 is another natural developing move. 3...Qg6 (forking the e4-and g3-pawns) 4. O-O is the La Bourdonnais gambit. Black has a bad time if they accept 4...Qxe4 on account of 5. Bxf7+. Though named for La Bourdonnais, this gambit was also analysed by Greco.^[1]

White's other approach is to open the centre and offer a pawn for further development, 3. d4 exd4 4. c3 dxc3 5. Nxc3. White expects to extend their lead by gaining time on Black's misplaced queen, and the open position lends itself to the attack.

Gioachino Greco was one of the first to record and analyse chess games. 2...Qf6?! was among the lines he debunked.^[1]

This line is also known as the McConnell defence for James McConnell, who played it against his friend Paul Morphy.^[2]

Wikipedia has related information at Greco Defence.