DDG 4.Nc3 f5

4...f5 not only defends the e4-pawn, but also blocks the b1-h7 diagonal, typically dominated by White's bishop and queen. As a result, the game is more closed than in other variations, which probably suits Black, especially if he attempted to play the French Defence. The line is a bit similar to the Pöhlmann Defence of the BDG, which arises after 1.d4 d5 2.e4 dxe4 3.Nc3 f5.
W

5.f3

5.f3 (! [Minev]; !? =/~ [ECO])

A) 5...exf3 6.Nxf3 Nf6

Alternatives to 6...Nf6 have created lovely miniatures:

B) 5...Nf6

W

C) 5...Bb4 6.Qb3

D) 5...e5 transposes.

5.Be2

5.Be2

5.Bf4

5.Bf4 [Schwarz] is a natural waiting move. Note that the bishop is quite pointless on g5 because h6 cannot be met with Bh4; besides, Nf6 is not a target because f5 blocks Rf1 out, and prevents Ne4.

Various