Spades - Strategy for Nil Vs. Nil round

Question

In the game of Spades, if two players from opposites partnerships bid 0 (Nil)^[1], then the round plays very different from a regular round, each of the non-Nil players try to set the opponent Nil without setting her partner.

Except maybe the first trick, only cover-players will lead tricks (since nilers avoid winning tricks, and if a nilers wins a trick the round become a single nil round).

The nilers are adjacent. This gives advantage to one partnership:

• the cover-partner that plays before both Nilers, has a disadvantage, she don't know if she should play high card to cover her partner or she can play a low card to try setting her opponent's nil.
• The cover-partner that plays after both Nilers has an advantage since she can see if she needs to cover or not.

I build an AI player of Spades, and I want to add this special case of Nil Vs. Nil round. My question is, what are the main strategy considerations, or what adjustments in game play should I add? For refining reasons, assume its the first round of the game^[2].

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[1] Nil Vs Nil rounds are not too rare in normal games. In the Suicide variant, every round is a Nil Vs Nil round.

[2] Occasionally, Nil Vs. Nil rounds happens at a "game winner round", that is to say, one partnership will win the game if she makes the Nil. In this kind of situations, other considerations come in to play. In order to refine the question, assume this is the first round of the game.

Answer 1

Some of the strategy will depend on the bids of the non-nil players. In Suicide Spades, the non-nil players must have each bid at least 4, but that could still be anything between 4 and 13. A bid of nil is equivalent to a bid of 10 in terms of points (100 if you win, -100 if you lose), so a non-nil player who has bid in the realm of 10 is as concerned with making their bid they are with protecting their partner's nil bid. Meanwhile, a player who has bid in the realm of 5 is much more concerned with protecting their nil bid partner. Bags are also a concern, as bags are worth up to -10 points each.

For the sake of the rest of the discussion, let's call the players A, B, C, and D, where B and C are the ones who made the nil bids, so A and D are leading rounds after the first (unless one of B or C takes a trick). Here are some specific considerations:

• D has the benefit of going last in some rounds, which A never has. Thus, D should keep some low cards to be able to capitalize on the situation where C has played the highest card.

• C has the benefit of playing after B each round, and thus can play the highest card still covered by B each round. This positional benefit may rival D's.

• A and D, by leading far more often than usual, have a much easier time getting a void in a suit, and probably want to do so, as this allows them to use a spade on that suit or lead spades to allow their partner to get rid of any spades. The risk of this is if they lead a low card, one of the two nil players is more likely to take the trick, but it's not necessarily clear which.

• It is especially important for A to get a void if A wants to lead spades, as D can reduce A's options by not breaking spades.

• If either of A or D knows that their partner has a void in a suit, they should definitely lead low in that suit, as this has a decent chance of forcing the other nil bid player to take the trick.

• If you are playing suicide spades, or are playing regular spades and two players have already made nil bids, you may want to bid several higher than you were originally planning, as multiple players will be actively avoiding taking tricks.

Answer 2

Tyler Wong wrote a short strategy guide for Spades, he briefly adress the Nil Vs Nil situation:

Trying to cover a nil while trying to break your opponents' nil or coverer is very difficult, especially if the opposing nil bid is on your left. If the opposing nil bid is on your right, you will often be able to see the plays of all three players before playing, which is very advantageous. The main principle is obvious: lead suits or cards you know or suspect are better for your partner than for the LHO.

He also think that the B-D partnership has the advantage

Answer 3

I play quite a bit of blind bid nil games online that give 200 points for nil and go to 1000. I have become something of a nil specialist, winning well over half of my games and often without taking a trick. As for being B or C, it is nice to see what the trick-taker of the other side has played on every trick, but it really doesn't make any difference as I routinely make it regardless. We trade 2 which makes it too easy, really. Certainly shouldn't be worth 200. 100 would be more realistic. Trading only one would lead to a fair amount of sets, which might not be all bad, but I don't know as I have never tried it.