One of the challenges we face in preparing for the fantasy football season is attempting to balance past results with future expectations. Some past performances are skill-based and are strong indicators of future performance. Others, however, are more rooted in luck. Knowing in which category to place each component of a player's performance can go a long way towards correctly setting your expectations heading into the season.

An area that might help point you in the right direction for your quarterback expectations is downfield passing performance.

The ability to lead a deep passing attack often makes for an elite fantasy football weapon. We've seen quarterbacks such as Patrick Mahomes and Matt Ryan put up big numbers with their deep ball in recent years. However, if a player is relying too heavily on the downfield passing game for fantasy numbers, it appears to make them a more unstable player moving forward.

The Study and Results

To study the impact of downfield passing numbers on fantasy stats, I looked at all quarterbacks with at least 200 attempts during the 2015, 2016, and 2017 seasons. Using data from Sports Info Solutions, I calculated each quarterback's percentage of fantasy points gained on the deep ball (throws of at least 20 yards downfield).

Of the 105 players in this study, the average quarterback earned 17.3 percent of his fantasy points on the deep ball. However, the range spanned from 4.1 percent (2016 Blake Bortles) to 37.7 percent (2017 Tom Savage). As you can probably guess from those two names, being on either extreme end of the spectrum isn't a great indicator of future fantasy success.

The first number that proved significant in this study was the 17.3 percent average. Among the quarterbacks who picked up more than 17.3 percent of their fantasy points on the deep ball, 65 percent saw a decline in their fantasy points per game the following season. Even more concerning: 40 percent saw a decline of at least three fantasy points per game.

This trend, predictably, also appears to impact players at the highest level to an even more extreme degree. Among quarterbacks who gained at least 22 percent of their fantasy points on the deep ball, 83 percent saw a decline in production the following year, by an average of 2.3 fantasy points per game.

Why does this trend hold true at such a high rate? On the field, throwing a quality deep ball is a skill that can be repeated year after year. Turning those throws into fantasy points, however, is highly based on luck. Whether those deep balls turn into touchdowns is largely out of the quarterback's control, and a few 40-yard scores can dramatically affect fantasy output. So when those high-scoring plays regress back to expectations, we're seeing those players' fantasy production come back down to earth as well.

So the next question is: who do we need to be wary of this year?

What It Means for 2019

In 2018, 16 quarterbacks gained more than 17.3 percent of their fantasy points on the deep ball, making them likely candidates for at least a small regression. That includes last year's fantasy darling Mahomes, who checked in at 19.3 percent. The quarterbacks we're most concerned with, however, are those at the highest level of exceeding expectations.

In 2018, seven quarterbacks landed above the concerning 22 percent threshold:

As previously mentioned, players in this category have seen an average decline of 2.3 fantasy points per game the following season. But what do these numbers really mean? Should we be avoiding these quarterbacks in our fantasy drafts?

As with any analytical study, these numbers can only tell us who is likely to decline. It's not a guarantee. Context always matters, so here's a closer look at a few key names and some thoughts on whether we should be concerned by their deep ball numbers:

Ben Roethlisberger - Big Ben stands out as the most obvious candidate on this list to suffer a steep drop-off. Not only did he benefit from an unsustainable deep ball performance but he lost Antonio Brown, who led Pittsburgh with 12 deep ball receptions, including 8 touchdowns, according to Sports Info Solutions. As a side note, Brown's 8 touchdowns on 12 deep receptions (an obviously unsustainable touchdown rate) is a perfect demonstration of the luck component to fantasy points in the deep passing game.

Russell Wilson - Picking up 26.5 percent of his fantasy points on the deep ball last year, Wilson stands out as another candidate for decline. In the years analyzed for this study, 10 quarterback posted a rate of 25 percent or higher. None of them increased their fantasy output the following season. It's also possible Wilson will suffer from the loss of Doug Baldwin, who finished third on the team with 6 receptions on 14 deep ball targets in 2018. Maybe second-round pick D.K. Metcalf will replace that production, but it's always hard to predict how a rookie receiver will fit in.

Baker Mayfield - Mayfield is a more complicated name on this list to analyze. With the third highest rate in the league, he stands out as a strong candidate for decline, but does the addition of Odell Beckham change things? Given the addition of Beckham and offensive coordinator Todd Monken, who is known for his downfield passing attack, it might be reasonable to ignore Mayfield's placement on this list. He also won't have to deal with a midseason coaching change, and that stability could also allow him to be an outlier to this statistic.

Drew Brees - You're probably tempted to believe a quarterback like Brees achieved his deep ball success with pure skill, but even future Hall of Famers aren't immune to a little luck factoring in. Check out Brees' deep ball stats in recent years via Sports Info Solutions:

Nearly one out of every five deep ball attempts by Brees resulted in a touchdown last year (9 of 50), an obviously unsustainable pace. Of course we should still expect another strong year from Brees, but we have to assume he won't replicate these deep ball numbers which should lead to a slight decline in his overall fantasy output.