BS strategy

I’ve played BS a handful of times, and I don’t think anyone plays it very strategically. This makes sense, because it’s a card game for 12-year-olds that’s more about making funny bluffs¹ than actually winning. But there is a strategy to it.

Rules recap

Play with 3+ people. Ideally 4-6. Pick a starting player and deal an equal number of cards to every player. Then the starting player plays N cards from their hand face-down and says, “N aces”. Anyone else can say BS. If they do, reveal the N cards the starting player played, and if they were aces, the BS-caller takes the pile. Otherwise the person playing the aces takes the pile. This continues clockwise through the ranks. The person to their left plays twos, then the person to their left plays threes, and so on. After reaching kings, cycle back to aces. The game ends when someone runs out of cards.

Example game:

• Player 1 puts down two aces and says, “two aces.”
• Player 2 puts down a three and says, “one two.” Player 4 calls “BS”. Player 2 takes the pile (the ace and the three).
• Player 3 puts down a six and a queen and says, “two threes.”
• Player 4 puts down a four and says, “one four.” Player 2 calls “BS”. Player 4 smugly reveals the four and Player 2 takes the pile (the six, the queen, and the four).
• Player 1 puts down a five and says, “one five.”
• And so on, until someone runs out of cards.

The strategy

It’s predetermined what ranks you will have to play. The starting player in a four-player game will always have to play aces, then fives, then nines, then kings, then fours, then eights, and so on. Know those ranks so that when you bluff, you know which cards you will need soon.

The second strategy pertains to when you should call BS. This will partly rely on your read of whoever is playing, but it also depends on how high your risk tolerance should be. Calling BS is a risk, and calling it on a bigger pile is a bigger risk (with a bigger potential reward). Here’s what determines your risk tolerance:

• You have a big hand. You’re behind, so you need to take risks to catch up.
• You don’t have the cards you will need for your last few plays. (It does you no good to get down to one card if it’s not the one you need, since someone will always call BS when you play your last card.) It takes some judgment to estimate how many more plays it is until your last one.
• The player playing has a small hand. They are close to winning and you need to stick them with some cards. (Also, a small hand means it’s less likely they have any particular card).
• Your turn is soon and you will have to lie. It reduces the size of the pile you’ll have to take if someone calls your lie, and if your BS call is wrong, the pile might have the card you need.
• There are fewer players. Punishing one player out of four is better than punishing one player out of six. And if there are more players, it’s more likely someone else calls BS and you don’t have to. Not that I’m suggesting you should delay calling BS for an advantage…

If you have a lot of cards, you might end up with enough to guarantee that a person’s claim is wrong (say, if you have all four jacks). Likewise if someone plays four cards at once, don’t call it unless you can disprove them, because if they’re lying then someone must have proof.

If you’re really good, I think you could count cards. Not perfectly, but if someone calls BS on two sevens and is wrong, you at least know they have two sevens. But I don’t think it would make a big difference.

How much can you win like this?

The average player of this game is not even paying attention to what other people play half the time, so just by doing that I think you have a slight advantage. And if you execute this strategy well I think you would have a large advantage over average player, maybe winning half the time in a four-person game. I don’t think that hard when I play and from a small sample size I think I win more than my fair share, but it’s hard to tell.

I would be curious to see how the game would look if everyone played it strategically. I think there would be fewer very short games (because anyone with an early lead would get BS called on them more often) and fewer very long games (because within a few turns everyone would have an endgame plan). I would like to make bots to do this, but game theory is hard so instead I’ll just think about it.