The Modern Defense (also known as the Robatsch Defence after Karl Robatsch) is a hypermodernchess opening in which Black allows White to occupy the center with pawns on d4 and e4, then proceeds to attack and undermine this "ideal" center without attempting to occupy it.
The Modern Defense usually starts with the opening moves:
The Modern Defense is closely related to the Pirc Defence, the primary difference being that in the Modern, Black delays developing the knight to f6. The delay of ...Nf6 attacking White's pawn on e4 gives White the option of blunting the g7-bishop with c2–c3. There are numerous transpositional possibilities between the two openings.
The Encyclopaedia of Chess Openings (ECO) classifies the Modern Defense as code B06, while codes B07 to B09 are assigned to the Pirc. The tenth edition of Modern Chess Openings (1965) grouped the Pirc and Robatsch together as the "Pirc–Robatsch Defense".
White's strongest response to the Modern Defense is 2.d4, to which Black typically responds 2...Bg7. The main continuations are:
3. Nc3 d6 4. f4 c6 5. Nf3 Bg4 (the Standard Line, ECO B06)
3. c4 (ECO A40) d6 4. Nc3 Nc6 5. Be3 e5 6. d5 Nce7 (7.g4 will be answered by 7...f5 8.gxf5 gxf5 9.Qh5+ Ng6 10.exf5 Qh4 11.Qxh4 Nxh4 12.Nb5 Kd8)
Other possibilities include:
3.Bc4 (Bishop Attack)
3.Bd2 (Westermann Gambit)
3.Bd3 (Wind Gambit)
3.f4 (Three Pawns Attack)
3.g3
3.Nf3
Fischer's 3.h4!?
Bobby Fischer suggested the move 3.h4!? as an unorthodox try against 1...g6 2.d4 Bg7, in his annotation to a game against Pal Benko.[1] (Fischer played 3.Nc3 in the actual game.) The idea is to pry open Black's kingside by h4–h5 followed by hxg6, as ...gxh5 would greatly weaken the cover to Black's king.
Averbakh System
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Averbakh System
The Modern Defense, Averbakh System (ECO A42) can be reached by the lines:
1.e4 g6 2.d4 Bg7 3.c4 d6 4.Nc3 (diagram)
1.d4 g6 2.c4 Bg7 3.Nc3 d6 4.e4 (diagram)
Possible moves for Black at this point include 4...Nf6, 4...Nc6, 4...e5, and 4...Nd7. The move 4...Nf6
leads to a position of the King's Indian Defence, where White has options 5.Nf3, 5.f3, 5.Be2, 5.f4, and so on.
Unusual White responses
The flexibility and toughness of the Modern Defense have provoked some very aggressive responses by White, including the crudely named Monkey's Bum, a typical sequence being 1.e4 g6 2.Bc4 Bg7 3.Qf3. (A more refined version is the Monkey's Bum Deferred, where White plays Bc4 and Qf3 only after developing the queen's knight.)
Unusual Black responses
Other unusual openings can be reached after 1.e4 g6. The Hippopotamus Defence is one such system. Another is the Norwegian Defence (also known as the North Sea Defence) which begins 1.e4 g6 2.d4 Nf6 3.e5 Nh5. (If White plays 4.g4, Black retreats the knight with 4...Ng7. On 4.Be2, Black can retreat the knight or gambit a pawn with 4...d6!? If White plays 3.Nc3 instead of 3.e5, Black can transpose to the Pirc Defence with 3...d6 or continue in unconventional fashion with 3...d5!?)
Transpositions
Transpositions are possible after 2.c4, for example a Maróczy Bind results after 2...c5 3.Nf3 Bg7 (or Nc6) 4.d4 cxd4 5.Nxd4 and the Averbakh system is reached after 2...Bg7 3.d4 d6 4.Nc3.
After 2.Nf3, Black can play 2...c5, transposing to the Sicilian Defense, or 2...Bg7. Following 2.Nc3, Black can transpose to a closed Sicilian with 2...c5 or play 2...Bg7.
