For my beginning students this week, I wrote three rules for castling on the whiteboard. When these three conditions are met, it is legal to castle. Castling moves two pieces--king and rook. It is the only way a king can move more than one square, and is the only time that more than one piece may be moved on a player's turn. In most games, it is a necessary precaution to decrease the vulnerability of the king. Castling has the added benefit of bringing a rook closer to the center, the usual scene of the battle in chess.
1) It must be the first move for both the king and the rook.
2) There must be no pieces between the king and the rook.
3) The king may not castle out of check, through check, or into check.
To illustrate the benefits of castling, I presented the following miniature from Greco. It was published in Francis Beale, The Royall Game of Chesse-Play (London, 1656). I take it from that source. Beale's version of this game differs at Black's move 18 from the one published in the more widely known Professor Hoffman [Angelo Lewis], The Games of Greco (London, 1900). Hoffman's version is the one found in David Levy, and Kevin O'Connell, Oxford Encyclopedia of Chess Games, vol. 1 1485-1866 (Oxford, 1981) and in databases.
Gambett VI (Greco) [C54]
1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.c3 Nf6 5.d4 exd4 6.cxd4 Bb4+ 7.Nc3 Nxe4
White to move
White meets all three conditions listed above. This notation means that White's king moves two squares towards the rook, and then (or at the same time), the rook moves to the square that the king moved over (see next diagram).
8...Nxc3 9.bxc3 Bxc3 10.Qb3
Black to move
Black's last chance to survive was 10...d5.
After the greedy rook grab, Black is materially ahead a rook and two pawns, but is completely lost due to the king's vulnerability and White's well-coordinated pieces. White may be down material on the whole board, but in the battle White has a substantial and decisive material advantage.
11.Bxf7+ Kf8 12.Bg5 Ne7 13.Ne5 Bxd4 14.Bg6 d5 15.Qf3+ Bf5 16.Bxf5 Bxe5 17.Be6+ Bf6 18.Bxf6 gxf6
Hoffman and database have 18...Ke8 19.Bxg7 1-0
I also showed the students a possible variation beginning with 18...Qd6. In this line, there is no immediate checkmate, but White wins back all of the sacrificed material and more, reaching an easily winning endgame.
19.Qxf6+ Ke8 20.Qf7# 1–0
My advanced students worked in pairs on a worksheet that I created last spring for a chess camp. It is elsewhere on this blog: "Incomplete Miniatures".