Thursday, August 23, 2012

Should You Pair Your Opponent's Lead?

Talk about a classic cribbage question! Should you pair your opponents lead, or is that sly dog planning to sneak in a three-of-a-kind on top of your pair for a big six points? If you stay up late pondering these questions you're in luck: we've got some data to help ease your mind. A word of caution, though. Today's post is nothing but numbers. If you just want the executive summary skip to the bottom of the post.

Before we show the numbers, let's talk about what we're measuring. We looked through our games and found all the hands (hundreds of thousands of them) where the dealer had the opportunity to pair their opponent's lead. We didn't include hands where the dealer could score a 4-of-a-kind in response if the non-dealer scores 3-of-a-kind. In those cases we'd consider the dealer the trapper, not the trappee. We did, however, include hands where the dealer had two cards 8 or higher, since the count would have to go past 30 for them to score their 4-of-a-kind. Perfectly clear? Then let's see some data:

Probability dealer would be trapped if they paired opponent's lead

Lead cardTrap %
A49.9%
237.9%
326.9%
423.3%
545.2%
635.4%
731.9%
828.5%
934.0%
1034.6%
J35.4%
Q31.8%
K32.1%
(Don't use these numbers, though. We've got more useful stuff coming up soon).

So if you're the dealer, you're sitting on an ace, and some random opponent starts play by laying down an ace, then there's a 49.9% chance that he's got at least one more ace in his hand.

The cut card has some bearing on these odds. If the you've got an ace, your opponent leads an ace, and the cut is an ace, then it's less likely that the your opponent has an ace in reserve. The normal case is that the cut card is a different rank than your opponent's lead. Let's see what the probabilities are in that situation:

Trap probability when lead is different rank than cut

Lead cardTrap %
A50.6%
238.8%
327.5%
423.8%
545.1%
636.3%
732.6%
829.0%
934.7%
1035.4%
J36.3%
Q32.6%
K32.8%
(Don't use these numbers yet, either)

Turns out that doesn't make that much of a difference. That's mainly due to the fact that the lead card is usually a different rank than the cut, though, so the averages are weighted heavily in that case's favor. We'll talk about the other case (lead is the same rank as the cut) a little later in the article.

What are the A players doing differently?

We talked a lot about the A players in our first post. Let's look at this first table to see what the A players are doing, and how we should respond to their fancy pants play:

Trap probability when playing A level players, lead different rank than cut

Lead cardTrap %
A47.4%
238.5%
328.9%
424.5%
552.5%
640.3%
735.9%
831.7%
944.1%
1041.6%
J44.3%
Q35.8%
K35.5%
Use these numbers!

The A players are less likely to try to trap with aces or twos (especially aces), but more likely to try to trap with everything else, especially nines and jacks. We see two lessons here: one is that the A players are more likely to lead from a pair, and that's a good sign that we should do that, too. Another lesson is that we should be nervous about pairing a good player's lead.

What if an A player's lead is the same rank as the cut?

Trap probability when playing A level players, lead same rank as cut

Lead cardTrap %
A29.4%
216.2%
317.8%
412.5%
5-
624.0%
713.0%
814.4%
923.4%
1019.4%
J16.4%
Q17.9%
K20.3%
(Note that we've left out statistics for the "5" case. We've got a lot of data, but that particular situation is so rare that we don't have a large enough sample to feel confident reporting on it)

The lead card is a lot less likely to be a trap when its the same rank as the cut. In particular, notice that all the probabilities are lower than 33%.

How should we play against A+++ players?

The keys to taking your game to the A level are study and practice. Getting from A to A+++ is going to take psychology and creativity. Here's a fun story from DeLynn Colvert, four time national champion and author of Play Winning Cribbage, about a game against former national champion Duane Toll:
The game with Duane Toll was a 4th round match in the Grand National in Lincoln City, OR. With the score 2-2 best 3 of 5, Toll was dealing from about 28 out and I was standing about 23 out with first count. Toll has studied my habits consistently leading from a pair. My hand was 3-3-4-k and well short of game. I lead from the single 4!! Toll was also short of winning with first count the next deal and was forced to play offense...and he played a 3 on my 4 lead! I paired his 3 and knowing I consistently lead from a pair immediately played the 3rd 3 for 6!! When I played the 4th 3 for 12 he was stunned, threw his remaining cards in the air and conceded the match. I went to the championship and $5,000! Toll took home $200 for the 4th round! His play of the 3rd 3 was a good play as he would have been 15 or so short otherwise!
Colvert and Toll are possibly the two best players in the world, and it's great to see how they approach a decision as common as "should I pair my opponent's card?"

Executive summary

Should you pair your opponent's lead? This data is an important piece of the answer, but there are other factors to take into account when making a decision of this magnitude. If you need two points to go out then of course you should pair the lead. And if your opponent always, 100% of the time, leads from a pair then you should be even more cautious about pairing their lead.  Your current board position also plays a big part (We’ll talk more about that soon in another article).

But you'll frequently find yourself in a position where you don't have a read on your opponent and you'd like to take a chance at some points as long as you're more likely to come out with more points than the other player. That's where this data comes in handy.

In a large fraction of hands we're happy to take a guaranteed two points for ourselves as long as our opponent will average less than two points in response. That means we should take the pair for two as long as there's less than a 33% probability that our opponent is going to get three-of-a-kind for 6 in response.

When you just want to come out ahead in the exchange, the executive summary is that you should pair your opponent's lead of a 3, 4, or 8 (the three leads with a < 33% trap probability). And if your opponent's lead matches the cut you should feel free to pair it.

Have any insights you'd like to share on this topic? Questions about the data? Suggestions for future posts? We'd love to hear from you. Leave your comments below.


Editor's Note: This is a guest post by Aaron Harsh continuing the series on cribbage strategy and tips. Aaron lives in Portland, Oregon with his wife Stacy and daughter Audrey. He spends his evenings analyzing cribbage strategy for Fuller Systems, and his days analyzing television viewership for Rentrak Corporation's Advanced Media & Information group. You can play him on Cribbage Pro Online as user "aaronhars", or in person at American Cribbage Congress grassroots club #28 (Oregon's Finest).

2 comments:

  1. I would be interested in a blog post about the ways in which some players are able to achieve such a high rate of Double Skunks.

    Imagine the "skill" that must be necessary to win, say, more than 1% (or even 0.5%) of one's games by such a large margin.

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    Replies
    1. Thanks for the comment and suggestion. Since we don't track each player individually by their user names with this game play data, the best we could probably do is look at games that resulted in a double skunk in aggregate and see if there was anything remarkable about it. My "gut feeling" is that we would not find anything terribly interesting on the whole, but perhaps Aaron (the guy analyzing the data and writing these great articles) will have some ideas. If you request is for us to investigate a particular user that may be "gaming the system" in some way, then email support at support@fullersystems.com with the user name of the player(s) in question and we will look into it.

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