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We Found The One Edge Your NFL Bets Might Have Over Vegas

Vegas is notoriously hard to beat. But as the NFL season gets started Thursday, there’s some promise for gamblers in betting on projected team win totals. Half-win totals from 8.5 on down seem to be very solid bets to hit the over, even when accounting for the vigorish, or house margin.

Money-line data is only available for a subset of the years for which we have win totals, but using a curated data set covering 2003 through 2018 provided by FiveThirtyEight contributor Greg Guglielmo, I calculated the implied probability that a team would hit the over for each half-win total below nine wins and compared it to the actual win percentage of those NFL teams. Surprisingly, there appears to be an edge.

Vegas typically wants a healthy margin on its action — the vigorish on win totals averages about 30 percent. But blindly betting the over on half-point totals from 5.5 to 8.5 wins since 2003 is nearly a push, with the house netting just a percentage point edge. And if you were to bet any of the half-point totals where the under is favored (indicated by a money line that is positive), you would actually come ahead, beating the house by 3 percentage points. Put in a way more familiar to gamblers: If you bet $100 on each of the 110 half-point overs in the sample with positive money lines, you’d come out ahead $330.

So why is there a systematic undervaluing of teams with half-point win predictions? One possible explanation might be that the public isn’t exactly sure how to value them; half-point totals aren’t particularly intuitive to bet. Additionally, perhaps there hasn’t been a widespread interest in surveying historical odds and win predictions, so bettors may not be particularly aware of the lack of calibration of the closing lines.

I ran this finding by professional bettor Seth Burn, and he pointed out that half-point win totals with the under favored don’t appear to exist currently, so perhaps the edge has already been squeezed out of the market. Or perhaps it’s a phantom edge that never really existed in the first place.

Josh Hermsmeyer is a football writer and analyst.

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