What defensive patterns and structures are used in Bughouse and Crazyhouse? I've heard that castling is rarely useful, but what should be done instead? My defensive play usually boils down to huddling in the "turtle formation":
[FEN "2rqkr2/pppbbppp/2nppn2/8/8/8/8/8 w KQ - 0 1"]
Turtling exaggerated for dramatic effect
This is entirely ineffective and quickly results in mate.
How can I defend in bughouse?
In general, in a bughouse game, one of the players in the team attacks while the other team member defends. Thus, when the defender gets attacked, the attacker sacrifices a lot of material. This material goes to the other team member (attacker), who can the use the material to fuel their attack. Thus, the defender loses (or saves) the match. Defensive strategies are therefore very important indeed.
The key square is usually the f2-square for white (f7 for black). Let's focus on black defending, since that is usually the case. Thus, the f7-square is critical. White will sac a bishop on f7, drop a knight on g5 and something diagonal on f7, leading to a quick win. The basic idea is to defend with e7-e6, blocking the a2-g8 diagonal. Yet, white can drop a pawn on f5 or sac a knight on f7 and drop a second knight on g5.
The main problem is that white can drop a pawn on h6 and open up the g7 and f6 squares for attack. If black plays h7-h6, then white drops a pawn on g6, attacking on f7. If you have to castle, then usually kingside is preferred, since queenside is vulnerable to a heavy piece dropped on a8 followed by a knight getting to a7. Also, a white pawn getting to a7 with a black king on c8 is a killer. Kingside castling makes the pawn drop on h6 perhaps even more deadly. Also, h7 starts becoming an issue.
So, here are a few tips how to survive as black against white attacking:
FWIW, I am not a good bughouse player, but that may be more due to my poor blitz play.
It is better to be aggressive and attack in Bughouse, If you are attacking on both boards, you will likely win, and yet, both white and black have to be concerned with defense, as dropped pieces can start an attack out of thin air. The best defense is a good offense even more so in Bughouse.
Dropped pieces, sacrifices to draw the king out, and dropped pawn chains are the usual modes of attack. The six squares a knights move from your king, the back rank, and the f7 (f2 for white) are the key squares to occupy and guard.
Squares are more important than lines in Bughouse. Lines are easily blocked by dropped pieces and squares are easily used by blocked pieces.
Development is important in Bughouse like regular chess, both for attack and defense. Your pieces on the board are your first line of defense against dropped pieces.
You want to move as few pawns off their starting squares as possible, and try to play with pieces. Pawns on the attack are usually dropped.
Piece values are quite different than regular chess. Pawns are more important and long distance pieces less. Also, the values are even more dependent on the board position than in regular chess. I would give as an approximation P-1, B-2, R-2, N-2.5, Q-5
A piece in the hand is worth two on the board.
Castling has always worked well for me, but the pawns in front of the King should never be moved, even for a fianchetto. It gives the opponent targets for sacrifices and weakens the control of key squares near the King. A pawn or a piece would then have to be dropped defensively later to patch the holes ; it will waste a turn and let the opponent attack, which isn't something you want in bughouse.
