An error of judgment. White wants to keep the Knight pinned, but it was more important to prevent Black from Castling immediately. B - K B 4 would have done this.
| 10. ........ | O - O | |
| 11. O - O - O |
Bold play, but again faulty judgment, unless he intended to play to win or lose, throwing safety to the winds. The Black Bishop at Kt 2 becomes a very powerful attacking piece. The strategical disposition of the Black pieces is now far superior to White's, therefore it will be Black who will take the offensive.
| 11. ........ | R - K 1 | |
| 12. K R - K 1 |
White wanted to keep his Q R on the open file, and consequently brings over his other Rook to the centre to defend his K P, which Black threatened to win by P - K Kt 4, followed by Kt × P.
| 12. ........ | P - Kt 4 ! |
Now that the K R is in the centre, Black can safely advance, since, in order to attack on the King's side, White would have to shift his Rooks, which he cannot do so long as Black keeps up the pressure in the centre.
| 13. B - Kt 3 | Kt - K R 4 |