NFL 1st Half Unders in Primetime

Bob Voulgaris, newly minted director of quantitative research and development for the Dallas Mavericks, is easily the most famous NBA sports bettor out there (although he's now retired from sports gambling and just stays active on NBA Twitter). One of his original profitable strategies was exploiting how sportsbooks set their NBA over/unders for each half:

It all had to do with how most bookmakers set their halftime totals, the predicted number of points scored in each half of the game. Each half, of course, is its own discrete period of play, and the fourth quarters of close games can end in elongated foul-clogged stretches of free throws, timeouts, fast play and, hence, a burst of scoring. But incredibly, bookmakers at the time didn’t account for this fact; they simply arrived at a total for the full game and cut that figure roughly down the middle, assigning some 50 percent of the points to the first half and 50 percent to the second.

Back in 2015, a former coworker came across a similar phenomenon in NFL first half over/unders, resulting in a considerable edge in specific situations. His strategy was so successful that it started 12-0 during the 2015 season, until we promptly bet it heavily on all 3 Thanksgiving Day games that year and it went 0-3.

Nonetheless, I went back and analyzed the past 3 full seasons of NFL first half totals (2015-2017) and found that the strategy still holds up remarkably well. The under has an abnormal success rate in games in which the first half over/under is >= 21 points, and is even more magnified in games that occur in primetime.

	O/U >= 21
All Games	WIN	338
	LOSS	264
	Push	19
	Total	621
	Win %	56.15%

56.15% is a very good success rate, but this market inefficiency skyrockets when the game is in "primetime":

	O/U >= 21
Primetime Only	WIN	91
	LOSS	46
	Push	5
	Total	142
	Win %	66.42%

I'm considering "primetime" to be any game that is the only game on - so Thursdays, Sunday nights, Monday nights, the London games (Sunday mornings), or the miscellaneous Saturday games late in the season. In other words, not in the afternoon on a Sunday.

Why does this edge occur in those spots? Over the years we've settled on the theory that players aren't in their normal rhythm that they experience most other Sundays, whether that's due to a shortened/extended week of practice, or just the game day pattern extending into the night. Therefore, they start slow during the game, resulting in less points in the first half. Regardless of the reason, this strategy hits at almost a 2/3 clip (66.42%).

The threshold of only betting first half O/U of 21+ results in the most profitable yield, but these effects stand up regardless of the number, just at a lower success rate:

	ALL O/U
All Games	WIN	402
	LOSS	344
	Push	22
	Total	768
	Win %	53.89%
	ALL O/U
Primetime Only	WIN	104
	LOSS	64
	Push	6
	Total	174
	Win %	61.90%