5.Nc3: castling on opposite sides is variation 2 of 6 in the Petroff Defence course, a intermediate opening course for Black (ECO C42). It runs 18 moves and begins 1. e4 e5 2. Nf3 Nf6 3. Nxe5 d6 4. Nf3 Nxe4 …. White trades knights on c3, takes back with the d-pawn and castles long. White's plan is a pawn storm on the kingside. Black develops calmly, keeps the position closed and can castle on either side. In the lesson every move is explained on a board and then drilled; it is free.
Move by move
1. e4 – White takes the centre.
1... e5 – Black claims an equal share.
2. Nf3 – White develops and attacks e5.
2... Nf6 – The Petroff: Black attacks e4 in return.
3. Nxe5 – White takes the pawn.
3... d6 – Black kicks the knight before taking back the pawn.
4. Nf3 – The knight goes back.
4... Nxe4 – Black wins the pawn back. Material is equal.
5. Nc3 – White offers a knight trade and prepares quick development with Be3, Qd2 and long castling.
5... Nxc3 – Black takes. Going back with the knight would only lose time.
6. dxc3 – White takes back toward the centre. The d-file opens for the queen and the rook, and the c1 bishop is free.
6... Be7 – Black develops and prepares to castle.
7. Be3 – White develops and gets ready for Qd2 and long castling.
7... Nc6 – Black develops the last knight.
8. Qd2 – The queen joins the rooks. Long castling comes next.
8... Be6 – Black develops the bishop and keeps both ways of castling open.
The lesson goes on for 2 more moves, each with its explanation.
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