Chess Opening Theory/1. e4/1...e6/2. d4/2...d5/3. Nd2/3...c5/4. Ngf3

4. Ngf3, White keeps the central tension and defends the d4 pawn with the knight. This often transposes to positions in the 4. exd5 lines, though a few independent lines exist.

4...cxd4 is the most played move, and the move that players who take back with the Queen after 4. exd5 usually play. White can transpose to the main line Chistyakov defence with 5. exd5 Qxd5, but now White has the option of 5. Nxd4 to avoid those lines. After 4...cxd4 5. Nxd4, White has the threat of Nb5, threatening Nc7+ or Nd6+., e.g. 5...dxe4 6. Nxe4 Nf6 7. Nxf6+ Qxf6 8. Nb5 Na6 9. Nd6+ Bxd6 10. Qxd6±.

4...Nc6 is the second most played move, and the move that players who take back with the pawn after 4. exd5 usually play. Now White can play 5. exd5 and answer 5...Qxd5 with 6. Bc4. Play usually transposes to the main line with 5...exd5.

4...Nf6 is the third most played move. White can transpose to the Closed Tarrasch after 5. e5, or keep an open position with 5. exd5.

4...a6 is a rare option. Usually White responds with 5. exd5 or 5. dxc5.