Looker Blog : Data Matters

Fantasy Football: A Guide for Streaming Defenses

Colin Zima, Chief Analytics Officer & VP of Product

Oct 4, 2017

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If you’re streaming fantasy football defenses -- selecting a new defense week-by-week -- finding the right defense to start can be difficult.

While the projections are usually a decent starting point for picking a defense, I wanted to analyze data from the 2016 season to see if any additional insights or patterns could be gleaned, such as home vs. away games, time of the games and the day of the week the game is played.

First, let’s take a quick look at the distribution of scoring for defensive fantasy points during the 2016 season:

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Looking at the cumulative probability and the number of games in which defenses earned a particular score, the data shows that about half of the time (specifically, 51.4%) you can expect to earn 6 points from your defense.

Defenses are more likely to earn less than 6 points than they are to exceed it. 44.4% of the time defenses earned 5 points and 40.8% of the time defenses earned over 7 points. The huge skew towards the upside is in big thanks to 2016’s Kansas City 35 point day against the Jets.

When we look at the 2015 and 2016 seasons for projections vs outperformance, it looks like we have some pretty reliable adjustments we can make to Yahoo’s defensive expectations:

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The trend shows that the higher your projection, the more likely it is that your team will undershoot that projection. In other words, don’t hold your breath on actually getting those 13+ points projected for your defense.

Digging further into projected scoring, let’s try to figure out how much we should reset our expectations:

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In the above visualization, the colored lines represent a group of defenses which were projected to earn a certain amount of points (ex. the bright blue line represents defenses expected to earn 10+ points during a game). Since this is a cumulative distribution, the defenses under the 50% line are underscoring their projection

We see a similar pattern here, the teams with the highest point projection (ex. the bright blue line representing 10+ projected points) tend to underperform by 3-4 points.

As you go farther right along the x-axis we see the opposite for teams with the lowest projected points. The red line represents teams projected to earn less than 4 points, and we can see that these teams tend to earn slightly more points than projected.

The more extreme the projection, the more likely it is to be off. It looks like we can expect an extra point on the lowest estimates and a 3+ point regression from the highest estimates, so don’t rely on your defense to carry (or save) the day.

Now that we’ve looked at what to expect from defenses, let’s try to gain some actionable advice for selecting a weekly defense. Below, we look at 2016 defense fantasy performance by game day:

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Looking at the weekly breakdown, Monday night defenses consistently underperform. On average, they are below projections by almost 2 points (-1.73 to be exact).

By comparison, defenses playing on Thursday or Sunday marginally overperform by 0.50 and 0.05.

So, if you are trying to decide between two similarly ranked/projected defenses and one of the teams has a Monday night game, our advice would be to NOT select them for the week and instead pick a team playing on Thursday or Sunday. While a small difference, I think many of us have been in situations where that extra 1-2 more points would have made the difference.

Another factor to take into account when selecting a weekly defense is whether they are playing a home or away game:

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Looking at the data for the 2016 season, defenses who were playing at home are more likely to outscore their fantasy projection by .33 points. On the other hand, defenses who were playing away were more likely to underscore their fantasy projection by .-0.45 points. Again, if you have a good defense this should not change whether or not you start them. However, if you are streaming defenses this is one more factor to consider.

Taking into account game night and whether or not a team is playing on the road, be careful with away teams on Monday night!

Finally, let’s take a look at how the time that the game is played may or may not impact defense fantasy points. Specifically, let’s compare prime-time games to other game times and see what we get:

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In the visualization above we are comparing defense fantasy performance for games played during prime time to games not played during prime time during the 2016 season. Here we see that defenses playing during prime time tend to slightly underperform their fantasy projections, whereas defenses who are not playing during prime time are more likely to score above their projections (although, still not by much).

To bring all the defense data findings together….

The majority of the time (51.4%), defenses earned 6 points during the 2016 season. Defenses which are projected to earn top points (10 or more) tend score about 3 few points than expected, while the lowest projected defense (less than 4 points) tend to do slightly better than expected. Defenses playing on Monday nights, away, and/or during prime time also tend to do slightly worse than projected.

Again, if you have a great defense, you’re probably better off playing them no matter their game day or time. However, if (like me) you’re streaming defenses every week to see who has the most favorable match up, these data-driven tips from the 2016 season may just save you a few points...and a win or two.

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