| 7, | Kt—B3 |
| O—O—O |
(7) Again, White's only legal move is to avoid the check, but of the three ways to do it interposing another force between the King and the attacking man is the best play, so he moves his Knight to B3. The student sees at once that the KKt is the only one that can be moved into that square as the QKt. is out in the middle of the board. The Knight is now pinned as it protects the King from the Black Bishop, otherwise it would be in a position to capture the Black Queen.
Black, in his seventh move, castles with his Queen's Rook as the squares on that side of the board are vacant. In order to do this, he moves the Rook to Qsq. and then moves the King to the QBsq. on the other side of the Rook. Although Black has left his Knight en pris, castling is his correct play for it enables him to develop his Rook which is a more powerful Piece than the Knight, and as the White King stands on an open file, Black, in one
