What the Data Saw: NFL Week Five

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What the Data Saw- NFL Week Five

The Model’s Day

The model went 8-6-1 for a modest gain this weekend. As for the season, the model has performed as follows:

Each week I do a video with Razor that appears on Instagram. I have been on the show for three straight weeks. Each time I am asked to make five specific predictions. The model has gone 12-2-1 in three weeks. The five sides include two survivors, two prop bets, and one against the spread pick. Those results are not included in the above calculations, nor are they generally included in my weekly articles. 

I encourage you to watch that show every week. 

The Round Robin Teaser

Last week I suggested you take a five-team round-robin teaser. The ten bets went 6-4 for a modest profit of 1.2 unit profit. Here is how this approach had performed before this season:

This means that if you had followed this approach every week this season, you would have profited 32.6 units. I explain why this works in two parts below. In the first section, I just provide a short answer. In the second section, I show you the math.

The Short Answer

First, teasers only have a positive expectation if used on the spread and across both the numbers three and seven. If you bet teasers any other way, you might as well burn your money. It will not work long-term. 

Second, by crossing three and seven, you gain a 23.46% win percentage in every single game. No matter what. This is because of the frequency with which the final margin of victory is 3, 4, 5, 6, and 7. All numbers you capture in this teaser. 

If you are 51% to bet a team on the spread, it is a losing proposition as you need a win percentage of 52.4% to be profitable against a -110 line. In a two-team teaser -120 (you can still find some -110s) you need a 74% win percentage to be profitable. 

By crossing the three and the seven you can add your 23.46% to your 51% and then have a 74.6% win percentage on two-team teasers. That is a profitable winning percentage. 

Now, if you are over 52.4%, then do not bet a teaser. Just bet the game against the spread. If not, tease the games.

The Math

Teasers have become a trendy way to bet. Casinos encourage them because they are often misused. Compounding the problem is that the NFL is a short sample size league. Thus, individuals that misuse teasers but experience a variance (a positive outcome) tend to eschew the math. The math is sound. There is only one way to win long-term using teasers – teasing through the three and the seven. 

The basic math

In order to prevail on a two-team teaser at -120, you must win each leg at 74%. This is why:

 A -120 line has an implied probability of 54.55%. Here is how we know that: (in the following formula, I am using the price (-120), and the amount you could win, $100)

= -120/(-120-100)

= -120/-220

= 54.55%

So to break even, you must win a two-team teaser at -120, 54.55% of the time. 

The next question is how do we determine if two unrelated teams are a combined 54.55% to win. That question is easy. We take the individual probability that each will win and multiply them together. 

For example, what are the odds that you will flip a fair coin twice and get two heads? Since the odds of a head is 50%, we multiply: .50 times .50 = .25. We then divide 1 by .25, and we come out with 4. We can then determine the proper odds of two heads are 3-1. 

We do the same math for a two-team parlay, teaser or not. Since we need a combined win percentage of 54.55%, we can see .74 times .74 = 54.76%. 

Now that we agree on what is required to win a two-team teaser, how can we get our win percentage to 74% for both legs? Simple, we use the points we get from moving the line. Here is how we apply that in real life. 

The following table lists the percentage of NFL games that end on specific margins:

MarginOccurrencePct.
0110.002
12160.0398
22080.0383
38170.1506
42650.0488
51840.0339
63150.0581
75090.0938
81980.0365
9860.0158
103130.0577

Let us start with the worst possible idea. Suppose you move from -3 to plus 3.  This is generally called moving through zero. Here is why that never makes sense mathematically. You will pick up the -2, -1, 0, 1,  and 2. You push on three. If we add up the percent those numbers represent in the final margins, we have the value you are adding by teasing. You get the following:

3.83% +.3.98% + .2% + .3.98% + .3.83% = 15.82% 

Since you have to get to 74%, this only makes sense if you were 58.18% certain the side would win without teasing it (74%-15.82% = 58.18%). If you are 58.18% certain on a spread without the teaser points, just bet the side straight. You have an edge already.  

The math will similarly fail for every combination of points, except one – when you tease through the three and the seven. You can do this in either direction. I will assume we are teasing down from -7.5 to -1.5. In this scenario, we gain the following:

9.38% + 5.81% + 3.39% + 4.88% + 15.06%

For a total of 

38.52%.

I wish I could tell you that was the end of the math, and you get a 38.52% boost to your win percentage. You do not. 

To even consider this wager, you must have concluded that your side is slightly less than 52.4% (required win percentage on a -110 line) to win at +2.5. Let us assume you had it at 51%. So you are already incorporating some of this value in your analysis. In this case, that means you are including the likelihood of your team winning by more than 7, 6, 5, 4, 3, and 2. What you pick up in value is 23.46%.

I would encourage you to make liberal use of teasers. I would stick to 6 points and -110 or -120 at the worst. I would stick to two-team teasers. However, never tease unless you capture both the three and the seven as a win. Otherwise, you are wasting your money. 

About the author:

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I write about data and sports. I created my first model in 1997 using nothing more than Excel. Currently, I have data-driven models for the NFL, NBA, and World Cup Soccer.

Mathematics is the music of reason.
— James Joseph Sylvester, English mathematician

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