I had an idea for a type of stalemate: One side cannot move at all because the king is trapped and all of that side’s pieces and pawns are pinned. This means that that side has no legal moves, and thus it is stalemate.

I wondered how many pieces and pawns, for both sides, could be put in such a position that were nessacary. I define this as either pinning a piece, blocking a piece, or trapping the the opponent’s king. The final position must be legal, stalemate for one side, and be legally reachable.

The best I can up with is the following position

[FEN "b2q1bq1/1N1N1N1k/8/rP1K1P1r/8/1P1B1P2/q2q4/2q1q1qq w - - 0 1"]

Initially, I though that 16 was the limit, not counting the kings of course: A piece/pawn around a king in the middle of the board, and a pinning piece for each of those. But I found that by spreading out the pieces that I could fit in 4 more-necessary to trap white king.

CLARIFICATION: I suppose the position I am looking for is one with promoted pieces and where 8 pins are absolutely nessacary. In this case, how about without promoted pieces, and as such 4 nessacary pins? Is more than 28 possible in this case? I suspect that it is. (Of course, it would be nigh near impossible to stalemate the white queen!)

Is this the limit, 22 units, for a pinned pieces stalemate, within the rules I have made? Do note that you can have one piece of protection per each king escape square to inflate the number needed.

UPDATE: I have found that there are categories for this where the black king does and does not help trap the white king. Evargalo has done the second option with 28 units.

I have “found” another 28 units position for the first category of the black king having to help. I say “found because it’s more or less just a slightly edited version of Evargalo’s position.

This is legal as two captures of white pawns, one white queen, and one black pawn ensure that the position is legal, as they allow for black to get their four promoted piece and get white their promoted horse.

[FEN "qn1r2b1/1R1BkNp1/1p3bP1/rN1K2Br/P3P2p/nR1N1b1P/b2r1P2/8 w - - 0 1"]
  • I suppose you want to maximise the number of useful pieces, i.e. pieces that can't be removed without breaking the stalemate ? Hence it is not good enough to add a wPh4 or a BNa1 in your diagram ? – Evargalo Apr 5 at 15:11
  • A white pawn on h4 is useful-it adds one more piece that cannot move for the stalemates side. But bNa1 is a no nol because it is not trapping the white king nor pinning a white piece. So yes, use pieces is what I’m looking for. If you can improve upon my position, put it an answer then! – Rewan Demontay Apr 5 at 16:30
  • Since you seemed to have had an in this question, @Evargalo, perhaps you could answer it? – Rewan Demontay Apr 10 at 18:49
  • TBH, this task hurts a bit my sense of esthetics. It is usual to try to achieve a pattern with the least possible units, but to maximize the number of pieces is much less appealing to me. In this case, I wouldn't be surprised if you could include all 32 pieces (or 31, without the wQ), but with a lot of black pieces that could be replaced by one or two more effective ones, and useless blocked wPs. – Evargalo Apr 10 at 20:06
[FEN "qn1r2b1/1N1BpRn1/1p3bP1/rN1K2Br/P3P2p/nR1N1b1P/b2r4/k7 w - - 0 1"]

Here is an (ugly) suggestion wth 28 units.

White is stalemated with 8 pins; removing any Black unit would break the stalemate.

White has promoted one of her three missing pawns (to knight) and black has promoted all of her five missing pawns (two into rooks, two into light-squared bishops, and one into a knight).

The four captures (white queen, 2 white pawns and 1 black pawn) ensure that this position is reachable. I am pretty sure we could add at least one of the missing pawns but that would require some retrograde analysis to prove the legality of the position that is beyond both my motivation and my available time. For instance, adding a white pawn on b2 doesn't work because it won't be possible anymore to promote all black pawns.

  • Can you link me a proof game that this is legal please as a comment at the least? I am unable to produce a 5th black passed pawn: apronus.com/chess/pgnviewer/… – Rewan Demontay May 16 at 12:58
  • @RewanDemontay I am afraid not... proof games are not my forte and it would take me way too much time. – Evargalo May 16 at 13:02
  • I don’t want an entire proof game. Just enough to see that 5 black pawns and 1 white pawn are passed. Then stop there. Is that good? – Rewan Demontay May 16 at 13:05
  • Also, supposing that the king must be involved, 28 units can be done: [FEN "qn1r2b1/1N1BkRp1/1p3bP1/rN1K2Br/P3P2p/nR1N1b1P/b2r1P2/8 w - - 0 1"] – Rewan Demontay May 16 at 13:09
  • Looking at it very fast, I cannot see either how I was intending to promote bPg7. To achieve 28 units, we just have to remove e.g. wPf2. – Evargalo May 16 at 13:12

Under the stipulation of 4 pins being needed, aka no promoted pieces, or "natural" pins, here's a maximal attempt of 30 in a legal position. While 31 is the theoretical maximum, all pieces minus the White queen, 30 is pretty close.

[FEN "4r3/1b1pB3/1nRP1pkb/pPp1K2p/PrB3pP/1P2PpP1/2R2P2/Nqn4N w - - 0 1]

Also, here's another 8 pinned pieces legal position of 28, but with no promoted White pieces, as a proof of concept of that certain idea. Now only if there was someplace to utilize that extra Black pawn... Additionally, the Black king is actually being useful.

 [FEN "3q3q/qn1Bp3/pR2P1p1/P3R1P1/1rNK1P1q/1PP5/2kB1N2/b2r1nqb w - - 0 1"]

Removing any Black piece and/or moving the Black king will instantly destroy the stalemate either diagram.

EDIT: At last, I have found legal 29-unit position for 8 pins, aka the limit, in which all Black pieces are vital! Removing a single Black piece or moving the King renders the stalemate nullified.

[FEN "q3r3/1R1p1p1q/1p1P1P1b/1Pk1BR2/1rN1K1Nq/p7/P1P1B1P1/1bn1q1nq w - - 0 1"]

The three missing White pieces ensure that the position is legal and that Black could have promoted all four of their missing pawns.

The Black g-pawn captured the White h-pawn to produce doubled pawns on the h-file. The h-file is now clear for two out of four pawns to promote.

The Black c-pawn captured the White queen to bypass the White pawn structure and promote. That's three out of four pawns.

The White e-pawn was captured and then Black e-pawn marched down and promoted . That's four out of four Black pawns promoted. Thus the position is legal.

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