Sac Chess

Here's a 10x10 variant maybe not so wildly different from chess, maybe computer-resistant to playing engines too, as far as giving reasonably skilled humans a chance against them. It's played on a large (10x10) board, which may help humans when vs. machines (e.g. as in standard 19x19 Go), and also the average number of legal moves per turn may be significantly greater than for chess, for instance.

Compared to the 'Grand Chess' 10x10 variant the start position is more orderly - there are no empty squares on both side's 1st/2nd rank (& start positions for the standard chess pieces are kind of retained). Fool's mate & a kind of Scholar's mate are both possible, as described in the Notes further below.

The name for the variant was inspired by the initials of the last 3 pieces on White's 1st rank. The density of pieces to empty cells in the setup is 60%, in a way no less close to that of orthodox chess (50%) than, say, Glinski's Hexagonal Chess (40%).

Three Game Courier presets for play are available thanks to Carlos Cetina, with all being rules enforcing.

Setup

JavaScript is disabled. Enable it to replace this static diagram with an interactive diagram.

  The White pieces are as follows (Black's are placed in a similar way):
  a1, j1: Chancellors; b1, i1: Archbishops; c1, h1: Sailors;
  d1, g1: Amazons; e1, f1: Missionaries;
  a2, j2: Judges; b2, i2: Rooks; c2, h2: Knights;
  d2, g2: Bishops; e2: Queen; f2: King;
  a3, b3, c3, d3, e3, f3, g3, h3, i3, j3: Pawns.

Pieces

There are 6 other piece types than in chess besides the standard 6 types:

Z = Amazon (moves like N or Q), a standard fairy chess piece

C = Chancellor (moves like N or R), a standard fairy chess piece made famous by Capablanca Chess

A = Archbishop (moves like N or B), a standard fairy chess piece made famous by Capablanca Chess

S = Sailor (moves like R or K), a piece from Shogi (promoted Rook, or Dragon King, in that game)

M = Missionary (moves like B or K), a piece from Shogi (promoted Bishop, or Dragon Horse, in that game)

J = Judge (moves like N or K), after a fairy chess piece also known as a Centaur

Rules

Apart from the differences already described above, Sac Chess is played like Chess with a few exceptions:

• Castling occurs on the 2nd rank between the king & either rook, with conditions as in chess.
• Pawns act standardly too (e.g. an initial 2-step move & en passant capture allowed), the only difference is that they still promote on the last rank, but any of the new types of pieces may be selected, besides the types allowed in chess.
• Stalemate, 3-fold repetition and 50 move rule all result in a draw, like in chess.

Notes

A game that might delight a beginner is 1 version of a Fool's mate: 1.Pg3-g5 Pf8-f7 2.Ph3-h5 Qe9-i5 mate. Then there is 1 version of Scholar's mate: 1.Pf3-f5 Pf8-f6 2.Bg2-d5 Nc9-d7 3.Qe2-g4 Nd7-e5 4.Qg4xg8 mate. Here's a sample Sac Chess opening possibility, besides the Fool's mate & Scholar's mate. It starts in a way like the Italian, Two Knights Defence, Wilkes Barre variation in chess:

1.Pf3-f5 Pf8-f6
2.Nh2-g4 Nc9-d7
3.Bg2-d5 Nh9-g7
4.Ng4-h6 Bg9-d6
5.Bxg8+ Ai10xg8
6.Nh6xg8 Zg10xg8

In my estimation Black has adequate compensation for his archbishop based on his lead in development. Here's the position after Black's 6th move:

Here's my tentative estimates for the relative values of Sac Chess pieces: P=1, N=3, B=3.5, R=5.5, Q=10, almost as in chess (note a 10x10 board increases the scope of the long-range pieces). My estimates for the new pieces in Sac Chess are: Z=14 (just as Q=R+B+P in value, Z=Q+N+P in value) C=9.5 (just as Q=R+B+P in value, C=R+N+P in value) A=7.5 (just as Q=R+B+P in value, A=N+B+P in value) Note a Z can mate unaided (and an A can possibly deliver mate to a K in a corner), which alone may not make Sac Chess a draw with perfect play. Also, I recall that a chess K has a fighting value of 4 (even though it cannot be exchanged); this value in my view might be rather oddly expressed (for lack of a known formula) as chess K = 32 x (max. # cells chess K moves to [eight]) divided by (# of cells on a chess board [sixty-four]) = 4; similarly, a Sac Chess K has a fighting value of 32 x (max. # cells Sac Chess K moves to [eight]) divided by (# of cells on Sac Chess board [one hundred]) = 2.5 approx. S=7.25 (only half a king's moves are added to a rook to make a sailor, & since Q=R+B+P in value, I'd say an S=R+(K/2-P/2)+P roughly in value, even though it's not at all royal) M=5.25 (only half a king's moves are added to a bishop to make a missionary, & since Q=R+B+P in value, so M=B+(K/2-P/2)+P in value) J=6.5 (just as Q=R+B+P in value, J=N+K+P in value).

Based on the above, a number of 1 for 1 piece trades could often prove equitable in Sac Chess games, i.e. Q for C, A for S, R for M, or B for N. Otherwise, there are many 2 for 1, 3 for 1, or 3 for 2 trades of pieces (perhaps including pawns) possibly equitable in Sac Chess. As in chess, pieces shouldn't be moved to squares where they are liable to be exposed to convenient attack by less valuable enemy pieces or pawns, if that then compels them to go to undesirable squares, or waste tempi due to retreating. The queens may thus take a while to activate safely, especially far from home, and that ought to hold true for many other valuable piece types in Sac Chess, which should often be more at ease once some of the correspondingly less valuable enemy pieces disappear from the board.

For more discussion of Sac Chess: Kevin's CFC Forum blog entry on Sac Chess

Note: to accommodate those who dislike the queen being clearly inferior to amazons both in their power AND in their number in Sac Chess at the start of a game, I can suggest the following fairly natural idea for a modified variant ('Royal Bevy Chess'), i.e. it has a similar setup and the same rules as for Sac Chess. Namely, in the setup position for Sac Chess, switch 2 queens for the 2 amazons, and switch an amazon for the single queen. This idea of having two queens and one amazon in a setup position may have first been used in Alekhine Chess, which is somewhat similar to Sac Chess, perhaps.

My own preference is to have the setup for Sac Chess as it is, as it was decided by my desire to stick to a basic compound piece "theme" by having 2 knighted Queens (i.e. Amazons) just as there are two knighted rooks (i.e. Chancellors), etc. That's as well as it being decided by my desire to have the traditional 8 piece array for standard chess embedded in each player's second rank, in conjunction with having two compound pieces on these ranks that would not be able to swiftly trade each other off. That could happen if each player moved such a piece so as to make a N-leap over the pawns on their respective 3rd ranks, and if 1 or both of these compound pieces (if placed symmetrically opposite each other) could move at the least like rooks as well, possibly allowing a trade.

Note that later Jean-Louis Cazaux independently invented the alternative variant to Sac Chess that I suggested be called 'Royal Bevy Chess', but he chose the name Heavy Chess for it, which seems a better name to me.

Last revised by Kevin Pacey.