Chess960 tactic on b7 (a6)
c9-11877naming tag (square·N)Opens in the app if installed, otherwise downloads the APK.
The tactical motive
Chess960 twist: use the unusual starting setup of the pieces.
Mate: a forcing sequence that ends the game — the king has no escape.
Mate in 4: a forced checkmate in four moves — every reply is covered.
A fork made possible by the Chess960 piece placement.
Difficulty 2350 ShuffleRating — expert level — few solve it at first try.
White to move — find the best continuation
How to recognize this tactic
In Chess960 the pieces start on unfamiliar squares, so tactics appear earlier and from unusual angles. Do not trust classical patterns — read the actual lines of the bishops, the rooks and the queen from where they really stand in this position.
This is a forced mating attack. Start from the enemy king: which of its squares are already covered, and which move takes away the rest while keeping the king in check? Forcing moves — checks and captures — are what turn an attack into mate.
A mate in four is a longer forced net: each of your moves is a check or an irresistible threat, and the king is driven step by step to a square where it is finally trapped. Verify that the defender has exactly one reply at every branch.
A set-up fork needs one preparing move before the fork lands — a check that drives the king onto the forking square, or a capture that lines the targets up. Find the preparation first, then the fork it makes possible.
General method: before you move, list the forcing candidates — every check, every capture, every direct threat — and calculate those first. The solution to a tactic is almost always among them.
Position on the board
White: king b1, queen a6, rook e3, bishop d1 a7, knight a5, pawn b2 c2 d2 h2 e5.
Black: king c7, queen h8, rook e8, bishop h4, knight e6 a8, pawn g4 h5 b6 c6 g6 d7.
11 white and 12 black pieces are on the board; the puzzle position arises after move 15.
The position in numbers
Black are ahead by 1 points of material (28 against 29; pawn = 1, knight and bishop = 3, rook = 5, queen = 9) — the tactic has to convert or outweigh that.
The white king stands on b1, the black king on c7.
It is White to move on move 15, with 37 legal replies to weigh — only the line that keeps the advantage solves the puzzle.
White keeps 5 pawns, Black 6. Files fully open (no pawns of either colour): a, f — natural highways for the rooks and queen. Half-open for White: g.
White hold the bishop pair, an edge in open lines. The White king has 3 empty squares to step to right now — the fewer they are, the closer a mating net.
Solution & explanation
Main line
15. Qb7+ Kd8 16. Nxc6+ dxc6 17. Rd3+ Nd4 18. Rxd4#
Why it works
- Great move! queen to b7 keeps the pressure (#3).
- Well found: knight to c6 (#2).
- Strong! rook to d3 is the sharp choice (#1).
- Best move. rook to d4 is exactly what the engine plays (#).
- The line ends in a forced mate in 4.
- If instead Kd8, then Nxc6+ and you stay on top.
Move by move
- 15. Qb7+ — queen to b7 with check
- Kd8 — king to d8
- 16. Nxc6+ — knight to c6 (capture) with check
- dxc6 — pawn to c6 (capture)
- 17. Rd3+ — rook to d3 with check
- Nd4 — knight to d4
- 18. Rxd4# — rook to d4 (capture) and it is checkmate
Types in this puzzle
Mate in 4+
A long forced mating combination.
Mate in four or longer is a marathon of forcing moves where the grip must never loosen. The tools are the same: checks, double threats and sacrifices that deny the opponent a single free tempo. Do not juggle the whole tree at once — walk the main line all the way to mate first, then verify the side branches. If somewhere the defender finds one quiet move that holds, your very first move was wrong.
Setup fork
The random setup allows a fork that classical chess never sees.
A setup fork is a double attack that exists only because of the unusual starting squares — in classical chess these targets never stand side by side. Look for pairs of undefended pieces on your opponent's back rank and for squares from which a knight or pawn hits both at once. Such forks usually appear within the first moves, before the pieces disperse. In every new position, note right away which starting pieces are defended by no one.
Sacrifice attack
Give up material to unleash a decisive attack.
A sacrificial attack gives up material on purpose to rip the king's shelter open and launch a decisive assault. The sac is sound when you get concrete assets in return: open lines to the king, tempi, pieces ready to pour in. The signs: a poorly sheltered king, your forces aimed at its home, defenders stranded far away. The iron rule is to calculate, not hope — once the material is gone, there is no way back.
About this position
These pieces come from starting position #381.
SP-381 · BastionScout — Off-centre king plus a rim knight (a/h): 168 positions carry this shape.
The king starts on c1, the rooks on b1 and e1, the queen on h1.
The king already stands on c1, so castling long moves only the rook, from b1 to d1.
The bishops stand on d1 and g1; their long diagonals reach h5 and a7 once the e- and f-pawns step aside.
One second-rank pawn starts with no defender at all: a2.
The setup belongs to the BastionScout family; read right to left it becomes position 296.
The engine's main line opens with f4.
Morozov Balance Index: 51 of 100 — class B — balanced. Engine evaluation of the starting position: +26 centipawns for White (depth 44, 400 000 000 nodes).
Explore position #381Provenance
Mined from the project's engine self-play games.
Pack 015 · SP-381
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