Photo: USA Today Sports

Gambling on the NFL is big business, especially after a 2018 Supreme Court decision striking down a federal ban on sports betting. Recent estimates suggest that as many as 46.6 million people will place a bet on the NFL this year, representing nearly one out of every five Americans of legal gambling age. As a result, there's been an explosion in sports betting content, most of which promises to make you a more profitable bettor. Given that backdrop, it can be hard to know who to trust.

Fortunately, you can trust me when I promise that I'm not going to make you a more profitable sports bettor. And neither will any of those other columns. It's essentially impossible for any written column to do so for a number of reasons I'll detail shortly. (I'm not saying it's impossible to be profitable betting on the NFL, just that it's impossible to get there thanks to a weekly picks column.)

This column's animating philosophy is not to make betting more profitable but to make betting more entertaining. And maybe along the way, we can make it a bit less unprofitable in the process, discussing how to find bets where the house's edge is smaller, how to manage your bankroll, and how to dramatically increase your return on investment in any family or office pick pools (because Dave in HR and Sarah in accounting are much softer marks than Caesar's and MGM).

If that sounds interesting to you, feel free to join me as we discuss the weekly Odds and Ends.

Let's Talk About the Unders

The vast majority of this column is devoted to betting against the spread, which is far and away the most popular type of bet in football. It has some neat advantages, the foremost of which is that Vegas is so good at its job that you're likely to hit on around 50% of your bets against the spread over a long timeline, no matter how good-- or bad-- you are.

Spread bets often have the smallest vigorish-- usually around 5%, which means you can expect to lose about 5% of the money you wager, albeit with very high variance from week to week. (If you wager around $300 a month, this comes out to about $15, which is approximately the price of a monthly Netflix subscription.)

We also discussed moneyline bets earlier this year, where you pick a team to win the game outright (regardless of margin), and your payout is based on the likelihood of that happening. Moneylines are not 50/50 propositions so they tend to be much "swingier" (you'll go on more runs where you're down big or up big over a short window), but they're cool because they dramatically simplify rooting interests.

The third main type of bet you can make on football is the "over/under" (or "o/u"). The sports book lists a point total, and you bet whether the teams will combine for more or fewer points than that total in a game (regardless of which team scores the points). You're essentially betting on whether a game will be more or less of a shootout than expected.

From a rooting standpoint, these are often less fun (most people watching football care more about which team wins than about how high-scoring the game is), which is why they tend to be less popular outside of parlays (a fourth bet type that we'll probably discuss later in the season). But there is one interesting quirk about them that sets them apart from spreads and moneylines, in my opinion: the "under" is the only bet that is expected to win more than 50% of the time over a long timeline.

"But wait," the fictional foil I just invented exclaims, "I thought Vegas was efficient; surely it can't be that easy to beat, can it?"

That's a very good question, person I totally made up just to advance the conversation, and thanks for asking it. Unders do tend to outperform overs, but not enough to make them profitable as-is. Remember our discussions of the vigorish or "vig" earlier this year, which is the way that Vegas tilts odds slightly in its favor to help ensure profitability. In a standard bet where the over and under both have odds of -110 (which means you have to bet $110 to win $100), your bets need to win more than 52% of the time to turn a profit. With a steeper vig, you need to win at a higher rate. Unders are slightly better than 50%, but not enough better to overcome the vig, which means Vegas still turns a profit.

Why do unders do better than overs? Because people love betting overs. Scoring is exciting, and rooting for more scoring is more fun than rooting for less scoring. Plus, with an "over" bet, you're usually still alive until very late in the game. You might have bet "over 44.5" and the game might only have 31 points late in the fourth quarter, but teams could always just score touchdowns on the next two drives, and there's usually at least a remote possibility of overtime to juice the total. Meanwhile, since points never come off the board again, "under" bets can be lost in the first half, leaving nothing to root for in the second.

(As a fun example, in 2013, the Vikings and Ravens played a game with an o/u of 41.5. As they approached the 2-minute warning in the 4th quarter, the teams had combined for just 19 points. They scored 36 points in the final 2:05 of the game and beat the over by nearly two touchdowns.)

Given that Vegas exists to maximize its profit, it makes sense that it'd shade things a hair so that the more popular bet loses slightly more often. Not quite enough for the "sharp money" to come in and take advantage, but enough to skim a bit extra off of recreational bettors.

Through six games last year, however, the unders were dramatically outperforming that 52-53% win rate; as I mentioned, everyone winds up seeing different lines, but by some sources, unders were 57-36-1 heading into Week 7, a 60.6% win rate that would have been very profitable for anyone who just mass-bet the under every week.

I drew attention to this and decided to track what would happen if we mass-bet unders the rest of the way. And while performance regressed (as it always does-- nobody is paying closer attention to Vegas' performance than Vegas itself) it technically wound up being profitable-- if we put an equal amount on the under for every game for the rest of the season, we would have won 53.1% of our bets and, assuming we were always betting at -110 odds, turned a 1.5% profit. (At $10 on every game, that would be a cool $26.36 in our pocket at the end of the year.)

This year (in part thanks to continued declines from the passing game), unders are off to an even hotter start, going 58-34-1 (relative to the posted "Lines I'm Seeing"), a 63% win-rate. If you had put an equal amount on the under in every game so far, you'd have been profitable in five out of six weeks and be up 20.1% over the year. (At $10 a bet, that's a $187.27 profit with $930 risked.)

(If you had instead started with a fixed bankroll of $160, let it roll over from week to week, and wagered an equal amount of that bankroll on every under every week, you'd instead be showing a profit of $166.26, albeit with less total money risked; yes, this value is different. We'll get to why later in the season.)

I wrote earlier this week that I expect passing offense to remain depressed going forward, so does that mean I think we should keep mass-betting unders? Not really. If I've noticed something and figured it out, you can be sure that Vegas has, so just because we would have had a 63% win rate over the last six weeks doesn't mean we'll have one over the next six. ("Vegas", remember, is a metonym for "the collective insight of people who wager on NFL games who set the betting lines through adversarial action".)

Does that mean that we shouldn't be betting more unders? Again, no. Remember, unders have a long-term structural advantage. Not enough to win you money in expectation, but enough to help you lose less money. And "helping you lose less money" is the best this column can aim for, so yeah, smashing the unders is an official Odds-and-Ends approved betting strategy. It might not help much, but it probably won't hurt, either.

Unless you think betting unders is boring. Gambling is best approached as an entertainment product with your losses as the cost, so there's no sense in "buying" bets you don't enjoy just because they "cost" slightly less.

I'd expect Unders to win roughly 50-53% of the time going forward, but I'll track it over the rest of the year and post the results.

Lines I'm Seeing