NFL Weak One and November Rain

I was literally on the plane when I saw A Lucky A Day's comment last weekend, and while I wasn't planning on spending my time this weekend on sports betting, one does what one can to keep one's readers happy. It's my last weekend before three weeks away, although plans are in a state of flux right now with one of my dogs getting sick while I was away for work last week, and currently hospitalised. If you've never owned a pet, it won't make sense that there is a possibility of cancelling a three week trip because of a sick dog, but some of you might understand. 

Anyway, the premise from Plus EV Analytics is that markets are inefficient early in the NFL season, and that backing big underdogs is a profitable exercise. As the positor concedes, one season doesn't prove anything but in 2018 the results were:

A +300 NFL 'dog is approximate to a team getting 7.5 points, but the selections above are teams getting 8.5 points or more, and backing these seven teams against the spread (ATS) would have produced a 5-2 winning record.

How about in previous seasons?

Looking at the past five seasons (2014-2018), the ATS record is 18-12, while over the past ten seasons (2009-2018) the ATS record is 40-38, which is a slender 0.1% ROI using Pinnacles -105 as our base. 

In Divisional games, the five and ten year records respectively are 8-2 and 18-11 which is a little more promising, and for Divisional games played on an artificial surface, the numbers are  3-1 and 10-4. 

To reset for a moment, since the current 32 team format was introduced in 2002, teams receiving more than 8 points have a losing (48.8%) record in the regular season.

Week One is, as might be expected, the most inefficient with a 17-9 ATS record for the big dogs. In Divisional games only, the record is 8-2 and in Divisional games on an artificial surface, the record is 100% from just the five games.

Here is a breakdown by week: 

It's interesting that the middle weeks of 8, 9 and 10 show an undervaluation of the underdog, especially on a grass surface, and the only rational explanation I can think of is that the bad weather is starting to impact the playing surface which drags the favourite down to the underdog's level!