Shortly before the NFL season, I wrote this piece highlighting a particular prop bet. Digging into the data behind this prop was my pet project (a nice word for obsession) last offseason, even though the actionable results ended up being fairly simple.
I was pleasantly surprised to find the “no” side of this prop being offered on almost every game at a flat +175, that left a lot more edge for us than anticipated.
Full disclosure: This is the first year I’m seriously betting this prop based on the data I gathered. Which means that the article ran without me knowing how the results would go moving forward. Let’s dig in and see how it’s done (roughly) one-fourth of the way through the 2021 NFL season.
The Betting Strategies
I’m going to evaluate these results two different ways. First, using a flat “one unit” bet, and second using adjusted bet sizing based on Kelly Criterion. If you’re unfamiliar, Kelly gives you bet sizes based on your bankroll, theoretical edge and risk tolerance. Using our Odds Calculator has been crucial in figuring out my edge (Kelly calculators require you to know it ahead of time).
I bet “full Kelly” on these, which would be over-aggressive if it were my only play on a weekly basis (or if I were a gambler with no other income), but the returns (in terms of units) are the same either way. This isn’t a discussion on bankroll management, but I’d suggest either flat-betting or half-Kelly if you want to tail me on these. The math behind finding the theoretical edge is also a bit more complex than we need to discuss here, but I calculated it very conservatively.
Flat Betting:
This strategy is extremely simple. Based on BetMGMs lines (no 3 straight scores at +175), we have about a 6% edge on any game that closes with a spread of less than 2.5. There’s a slight edge for games with a three-point spread (particularly if the total is low enough), but I wasn’t confident enough in the data to bet those.
So far this season, 15 games have closed at 2.5 or narrower (results may vary depending on book). I also haven’t been great about waiting until right before kickoff to place these bets, with DFS being the priority Sunday mornings, so some of them may have shifted slightly after bet placement.
This bet has gone 8-7 through the first 15 games of the season. That wouldn’t be great on a -110 side or total bet, but at +175, it’s a print fest. Flat betting this would have you up seven units through five weeks, or 1.4 units a week. This is far better than expected — I should have had a 15% edge based on the bets available so far. I’m bracing for some regression toward the mean moving forward.
Kelly Betting:
As referenced above, figuring out the Kelly math was a bit trickier. The earlier article mentioned that totals weren’t very predictive for this bet. When calculating bet sizing though, I factored them in. This was heavily sample-size dependent — I only factored in total when there was a large enough sample of games with similar spreads and totals.
Naturally, the result is the same 8-7 record obtained with flat betting. However, varying bet sizes based on edge has produced a profit of … 6.72 units. Either something is off in my edge calculations, or this tiny sample size has ran slightly poorly (at least relative to the overall positive variance).
Moving Forward:
I’ll continue to track results based on both methods and I plan on switching to betting flat moving forward. Varying bets probably does me no favors in terms of longevity here. With BetMGM being the only place I have access to this prop, that’s a concern. It has also under-performed betting flat, so there’s no reason to assume the extra risk.
For you, the actionable results here are extraordinarily simple. If you have access to BetMGM, anytime you see a spread within 2.5 you should bet it. Bonus points for lower total games, but I don’t think that’s a crucial point to focus on. I can’t promise anything moving forward, but the theoretical and practical results both suggest we have an edge here.
I’ll be checking back in around Week 10 or so to update results further. As always, feel free to get in touch if you have any questions, or (more importantly) know anywhere else offering this bet. Good luck everyone.
