Chess Opening Theory/1. e4/1...d6/2. d4/2...Nf6/3. Nc3/3...g6/4. f4/4...Bg7/5. Nf3/5...O-O

=Austrian Attack= 5...O-O is seen much more often than 5...c5. Now the black king has escaped the centre, so there is no major threat if White plays 6.e5 immediately.

White will likely play 6.e5, Be3, Be2 or Bd3 (the main line) later. His desire is to develop the minor piece, control the c8-h3 diagonal (with h3), and eventually push e5, getting more space.

Black may answer with 6...Na6!?. Although this move put his knight on the rim, it prepares for ...c5, create counter play on queenside. Other reasonable and more intuitive responses are 6...Nc6 or 6...Bg4, and then ...e5. Black must get either c5 or e5, or he will be in trouble later, due to having nearly no spatial advantage.

Theory table
.

1. e4 d6 2. d4 Nf6 3. Nc3 g6 4. f4 Bg7 5. Nf3 O-O