Chess Opening Theory/1. d4/1...d5/2. e4/2...dxe4/3. Nc3/3...f5

Instead of opting for the standard 3...Nf6 or even 3...Bf5, Black chooses to defend their e4 pawn with their f-pawn, an opening named the Netherlands Variation. This is inferior to other ways of defending the pawn as it weakens the kingside and creates a hole on e5.

White has many possible responses to 3...f5.

4. f3 is the standard Blackmar-Diemer way to continue, attacking the e4 pawn once more and usually looking for 4...exf3 5. Nxf3 where White develops yet another piece, but can be declined by 4...Nf6 defending the e4 pawn once more, this time by the knight. This is White's most popular continuation.

4. Bc4 and 4. Bf4 both develop the bishops, however they do nothing to take advantage of the weakened kingside or put pressure on the e4 pawn. They can both be met easily by the solid 4...Nf6.

4. Bg5 is the best and most aggressive move. It tries to discourage 4...Nf6, and springs a potentially deadly trap to exploit the weakened kingside if Black plays incorrectly. 4...Nf6 would be Black's best move, but 4...h6?? is way more common and falls into the trap: 5. Qh5+!, and 5...g6? isn't possible as the pawn on h7 that would usually guard it is now on h6, so 5...Kd7 is forced, and 6. Bc4+- rolls an attack on Black's king which Black simply can't defend safely.

The Netherlands Variation with 3...f5 can lead to many traps where White can get a crushing attack after 4. Bg5. The most popular example is 4...h6??, where after 5. Qh5+ Kd7 6. Bc4+- White has a crushing attack on Black's exposed king with the h6 pawn not being able to take the g5 bishop because it is pinned to the h8 rook by the queen on h5. 4...Nf6 is Black's best move after 4. Bg5 but can still fall for a trap after 5. f3 exf3 6. Nxf3. If Black thinks 6...h6? is safe now, 7. Bxf6! exf6 8. Nh4! will prove them wrong, usually leading to 8...Qe7+ 9. Be2+- as Ng6 forking the queen on e7 and the rook on h8 is threatened and 9...Qf7??, the most popular move, loses to 10. Bh5! pinning the lost queen to the king and the White queen on d1 defending the bishop.