This season, and the last few weeks in particular, have been decidedly one-sided when it comes to betting outcomes. The underdogs covered 21-of-30 games played over the course of the last two weeks. You can handicap all you want, but chances are pretty good that a trend that strong is going to wreak havoc on you. Overall on the season, the underdogs have covered 88 games, the favorites have covered 68 and there has been one push. That means that the underdogs have covered 56.4 percent of the games played. If you ignore the first two weeks of the season, the underdogs jump up to 58 percent covers.

It's not just that underdogs have been exploiting large spreads, either. Over the course of the last two weeks, 15-of-21 underdogs that have covered have won outright. In some cases the underdogs haven't just won, they have embarrassed their opponent. Chicago was favored over Miami by 13.5, but they lost by 18. The Jets beat the Pats when they were 10.5 dogs, Houston won when given 10 against Jacksonville and Cleveland won outright with nine points on their side. The underdogs are on a tear. There are two questions, then, that we have to ask. Why is this happening, and can we trust the trend to continue?

If you're having trouble picking winners this year, you probably have last season to blame. As dominant as the underdogs have been this year, the favorites were just as dominant last season. Over the course of the entire season last year the favorites covered 57.7 percent of the games. All you had to do was close your eyes and blindly throw your cash at the chalk and you ended up in the money. It was even more one-sided when the favorite was the road team. In that case they went 48-30-4, which is a 61.5 percent rate. If you got used to winning on the favorites last year it may have taken you a while to switch allegiances and jump to the underdogs.

The thing is that it's not this year that is an aberration. It was last year that was out of whack. Not only was last year the most decisive favorite advantage we have seen, it was just the second time in the last 20 years that the favorites have covered 53 percent or more of games. In other words, at the standard -110 bet, betting favorites has been unprofitable 18 of the last 20 years. So, what we are seeing this year is perhaps more extreme than we might expect, but it isn't completely unexpected. Instead of panicking too much about this season, you'd be better off forgetting that last year ever happened.

Why is betting the favorite so notoriously bad in the NFL? Basically, it's the public's fault. As much as 60 percent of all money bet on sports is wagered on the NFL, and two-thirds of that money generally goes towards the favorites. Fans like their teams, or they like the teams with the big name players, and they often have little regard for what the number is. It seems obvious, then, that lines that move are going to more often move further away from the underdog, which gives the dog more chance to cover. More significantly, if bookmakers know that a larger portion of the action is going to be on the favorite then they are going to make their spreads bigger than they would in a completely neutral environment in order to protect against exposure - a process called 'shading'. If you wanted to, you could look at it as if the underdogs were starting each game with an advantage of a half a point or more, regardless of the spread. That would account for why, in most years, the favorites are a bad bet.

Even if last year was a fluke, underdogs are winning at a very high rate this year. Let's look at some possible reasons why that is:

1) Hangover from last year - A lot of sportsbooks didn't make any money last year. People bet the favorites, and they parlayed the favorites, and they won. By many accounts, sportsbooks had to endure seven consecutive losing weeks at one point last season. Nobody likes to lose, especially when they are in the business of winning. Because the books were losing more when action was one-sided on the favorites, it seems logical that they would be looking to balance the action and get more on the underdogs to avoid a repeat of last year. That could mean that spreads are larger than they might otherwise be to make the underdogs more attractive. If linesmakers overcompensated as a result of last year's debacle, then that could explain the underdog success this year.

2) Blame the Internet - This is an extension of the last reason. It's not just that the favorites had such a heyday last year, but that everyone knows that the favorites had a great year last year. Because of the Internet, with its thousands of outlets for news, stats and information, more people are going to be aware of what happened last year. That could mean that even more people are backing the favorites in response to what happened than they normally would.

3) Relative strength - I could blame parity here, but that's just a lazy excuse. There are still some teams that are much better than others. The problem is that some 'bad' teams can play well in some spots. Two weeks ago, the list of the three best teams in the NFL would probably have been Indianapolis, Chicago and New England. Since then, all three teams have failed, by a wide margin, to cover double-digit spreads, and the Bears and the Pats lost outright. It may have been hard to see any of those results happen before the game, but when you look at the tape after the game it can make sense. All three of those dogs were able to disrupt the favored quarterback and slow down potent offenses. If those teams each played a five-game series then the better team would win almost every time, but in one game anything can happen, and this year it has.

4) Small sample size - Before we panic about what is happening, we have to remember that we are dealing with a very small number of games. There are, at most, 16 games per week. After 11 weeks we have only seen 157 games played. It only takes a few games on a sample that small to skew things. If the favorites had covered just one more game per week, which is not at all unreasonable, then the underdogs would have covered less than half the games played and I wouldn't be writing this article. If a trend like this were to appear three months into the NBA or MLB, with many, many more games played, then it would be much more interesting, and much more concerning.