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NFL Betting: Home Underdogs a Solid Strategy or Myth?

by - 9/7/2016

Robert Griffin III of the Cleveland Browns

People ask me for advice on NFL betting all the time. My first two suggestions are always the same: know your enemy and play against the general public.

The first thing that any football gambler has to admit is that the oddsmakers that set NFL lines are much, much better at their job than gamblers are at theirs. Not only do oddsmakers have a far greater understanding of the math involved - and this is where I note that my tagline at Doc's Sports is that "Gambling isn't magic - it is mathematics" - but they also have a keener instinct and understanding of the betting market.

A lot of people still think of the spread as some kind of predictive indicator. The oddsmakers aren't trying to predict anything. Instead, they are simply trying to produce a number that will generate balanced action on both teams so the sportsbooks cantake full advantage of the 10-percent edge - the vig - that The House has over The Player.

And these guys are good! How good? According to one online data generator, over the last 3220 NFL regular season games the favorites have gone 1596-1624 against the spread. That is nearly a perfect 50-50 split and anyone who had blindly bet $100 on every favorite over the last 13 years would be down nearly $10,000. Check and mate.

So these guys are sharp. But they are not unbeatable. Now, every bettor I have met thinks that they are The One Who Will Beat The Books. But ironically most individual gamblers herd together and groupthink when it comes to ideas on how exactly to win only to find that betting like Everyone Else has proven itself a losing proposition. So the second thing we need to do is figure out how Everyone Else is betting and go the other way.

For example, one of the longest-running myths in NFL betting is the undeniablepower of the home underdog. Time and time again I've heard square bettors toutthis idea. But last year NFL home underdogs went just 45-42 against the spread, just a 51.7 percent success rate. That 2015 record is also relatively close to the shallow 50.8 percent ATS success rate in this decade and the 48.9 ATS win rate for home underdogs over the last 12 years.

So betting on home underdogs, in general, is a losing long-term strategy. But even though these long-term numbers debunk one of NFL gambling's most widely held beliefs it doesn't stop every poser with a tip sheet parroting the myth that, "The sharps love a home dog."

Instead of following the crowd, truly sharp bettors are able to roll up their sleeves, dig through the numbers, and turn the oddsmakers strength into their own personal advantage. And while betting on NFL home underdogs is a losing approach in general, there are two specific instances where taking the points on the home team can be a successful long-term strategy.

The first theory is very basic and relatively rare: PLAY ON NFL home underdogs of 9.5 points or more. This system really speaks for itself. These are the ugliest of ugly home dogs and a team will only be catching this many points if they are one of the dregs of the league playing one of the NFL's powerhouse teams, like if Seattle plays at Tennessee.

Over the past five seasons home underdogs in this range have actually gone 14-8 against the spread. That's not a lot of trials and these situations don't crop up often (there were none of these games in 2015), but it is a solid 63.6 percent system. It involves holding your nose and taking a giant leap of faith with an overmatched team. But in the end it's a perfect example of going against the general public and, in essence, betting with the oddsmakers instead of against them.

But my main theory, pointed out to me by a long-time friend and of the few people that I actually discuss NFL betting strategy with, is to PLAY ON NFL home underdogs of 2.5 points or less.

Your first question might be, "Why 2.5 or less?" That's not some arbitrary number. And to understand it you need to understand the concept of "key numbers" in NFL betting.

Key numbers represent the most common scoring differentials in NFL games. Over the past 3,000 NFL games the final score has been a difference of three in about 19 percent of all games and the final score has been a difference of exactly a touchdown in nearly 12 percent of all games. For that reason, 3.0 and 7.0 are often considered the "key" numbers. Ten (7.6 percent), six (6.9 percent) and four (6.7 percent) are the next three highest occurring point differentials and also important numbers in terms of spread value.

Since they represent the two most common differentials, accounting for nearly one-third of all games, it is not an accident that the two most common NFL spreads are 3.0 and 7.0. This is also why getting games at 3.5 and 6.5 can drastically alter the statistical value and probability for your wager.

As I mentioned, the oddsmakers not only have a statistical advantage over the players but they also know HOW the players bet and WHO they want to bet on. And the books know that when they dangle a favorite out there at less than three points - like -2.5 or -1.5 - gamblers' first instinct is to look at the favorite because, hey, they don't have to lay a field goal and that makes instantly makes it a stronger bet, right?

Further, oddsmakers know that the general gambling public overvalues and disproportionally bets on favorites; they are favored for a reason, right? So the sportsbooksknow that the public likes betting favorites, they knowthe public overemphasizes the fact a team is favored, and they know they can bait action on these favorites by offering a line off of a key number. This is how oddsmakers lay the perfect trap for unsuspecting bettors: with subtle psychological manipulations rooted in strong math.

Not only are we not going to fall into this trap but we, the savvy sports gamblers that we are, can use this knowledge against the books and beat them at their own game.

Over the last five years betting on home underdogs of less than three points has gone 89-61 against the spread, including the playoffs. That is a healthy 59.3 percent success rate and near that magical 60 percent threshold that all gamblers crave. That's no shortage of trials either. I think 150 games over a five-year stretch is ample evidence that this system is a moneymaker and it has shown a profit in each of the past five seasons.

But we can do even better. And in my research I noticed a simple filter that increases the potency of this under-the-radar system. Betting on home underdogs of 2.5 or less in the first three weeks of the season has gone 18-9 ATS over the past five years, a 66.7 percent success rate! This system has also gone 22-12 (64.7 percent) in the first four weeks of the season and a solid 27-15 (64.2 percent) in the first five weeks of the campaign. If you had bet just $500 on each of these games the past five years you would be up over $5,200 in profit.

(There are other statistical filters that can be added to this system that increases its efficiency above 70 percent - but I can't give away all of my tricks!)

On the whole, there is nothing fundamental or situational that would create extra value on these home underdogs; this is purely a numbers-based system play. But, it does make sense that it would be so effective early in the year. There's always uncertainty in the NFL market early in the season on both ends; neither the books nor the bettors have a good grasp of the teams yet. The spread itself indicates that these matchups are essentially coin-flip games between somewhat evenly matched teams. And since bettors have a natural psychological tendency to bet on teams as they have performed in the past (in this instance, last season) rather than considering that a new season means that these are entirely unique teams it is even easier for both the oddsmakers and the gamblers to overvalue the team that's favored.

To be a successful sports bettor you need to be able to understand why the books are setting the lines that they do and how they expect the general public to react to those lines. And when you embrace the fact that the oddsmakers are very good at what they do and the gambling public is pretty bad at what it does you've taken the first step to setting yourself up for long-term success.

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