How good was Ryan Fitzpatrick's 2015 season? How good has he been since he first became a starting NFL quarterback in 2008? The easy answer is just look at his statistics. Many have called Fitzpatrick's 2015 season a "career" year. Some have even called it the best season ever by a Jets quarterback. By just looking at the raw statistics these statements are to a certain extent defensible. However, dig deeper and you may realize such statements are on pretty shaky ground.
Let's try to dig a bit deeper by normalizing Fitzpatrick's stats. What do I mean by that? Simply this: adjusting his numbers to account for the level of pass defenses he faced. After making such adjustments, we can then compare Fitzpatrick's adjusted stats to league averages for each year to try to make his raw numbers more meaningful in the context of both the level of competition he faced and the average level of quarterback play in the NFL at the time his stats were generated.
Let's first take a look at Fitzpatrick's statistics in the context of the level of defenses he has faced since 2008, when he first became a starting quarterback in the NFL. Here is a chart of Fitzpatrick's passer rating in each of the relevant years, the average passer rating of the defenses he faced in these years, and Fitzpatrick's "adjusted passer rating", calculated by dividing Fitzpatrick's actual passer rating by a fraction of which the numerator = NFL average passer rating for the year in question and the denominator = the average passer rating for the defenses Fitzpatrick faced in said year. For example, using nice round numbers, if Fitzpatrick posted a passer rating of 100 in a given year, but that rating was posted in a year when the average pass defense he faced was, say 90, while the NFL average pass defense allowed a rating of 100, then his adjusted passer rating for that year would = 100 divided by the fraction 90/100. That adjusted passer rating would then be 111, reflecting the fact that Fitzpatrick had amassed his 100 passer rating against significantly better than average defenses for that year. The chart of adjusted passer ratings for Fitzpatrick since 2010 is as follows:
Year 
Passer Rating 
Average Passer Rating Allowed By Defenses Faced 
NFL Average Passer Rating 
Fitzpatrick Adjusted Passer Rating 




. 
2008 
70.0 
78.4 
81.5 
72.8 
2009 
69.7 
79.6 
81.2 
71.1 
2010 
81.8 
82.4 
82.2 
81.6 
2011 
79.1 
83.9 
82.5 
77.8 
2012 
83.3 
83.8 
83.8 
83.3 
2013 
82.0 
86.8 
84.1 
79.5 
2014 
95.3 
92.6 
87.1 
89.7 
2015 
88.0 
92.4 
88.4 
84.2 





The idea of adjusted passer rating is to produce an approximation of what a quarterback would have produced if he had faced league average pass defenses; a "defense neutral" passer rating so to speak. If we then divide Fitzpatrick's adjusted passer ratings by the NFL average passer rating for each of the years in question, we get a number which reflects Fitzpatrick's passer rating compared to the average NFL quarterback for each year (by definition the overall average NFL passer rating was compiled against, in the aggregate, the average NFL pass defense). This number in theory reflects Fitzpatrick's effectiveness as a quarterback relative to the average NFL quarterback, with distortions related to the level of defenses he faced having been accounted for. We'll call this the % of NFL average. This stat reflects how much better or worse than average Fitzpatrick was in any given year, expressed in terms of percentages. A number greater than 100 here represents a better than average performance; a number less than 100 represents a worse than average performance.
Year 
NFL Average Passer Rating 
Fitzpatrick Adjusted Passer Rating 
% of NFL Average 



. 
2008 
81.5 
72.8 
89.3 
2009 
81.2 
71.1 
87.6 
2010 
82.2 
81.6 
99.3 
2011 
82.5 
77.8 
94.3 
2012 
83.8 
83.3 
99.4 
2013 
84.1 
79.5 
94.5 
2014 
87.1 
89.7 
103.0 
2015 
88.4 
84.2 
95.2 




As we can see after we adjust the numbers to reflect the context of defenses faced and NFL passer rating averages for each of the years in question, a somewhat different statistical profile emerges for Fitzpatrick. In particular, 2015 was in no way a career year for Fitzpatrick, after making the requisite adjustments in the numbers. In fact 2015 turns out to be one of Fitzpatrick's worst years since 2010. If we concede that Fitzpatrick's weapons in 2015 were a large improvement on any weapons he had in any other year except 2014, when he was throwing to Andre Johnson and DeAndre Hopkins, a good argument can be made that, relative to the average NFL quarterback, 2015 was in fact Fitzpatrick's worst year since 2010. Even if we don't adjust for the average NFL quarterback rating as reflected in the % of NFL Average number, Fitzpatrick's adjusted passer rating in 2015 was not as good as his 2014 number and was only marginally better than 2012 and 2010. Considering the large upgrade in weapons Fitzpatrick had in 2015 as compared to his Buffalo teams of 20102012, it's not difficult to argue that at best 2015 was Fitzpatrick's fourth best year in the last six, and depending on how much of a difference we assign to the improvement in weapons, arguably his worst.
It is worth noting that in Fitzpatrick's first two seasons as a starter he had some pretty bad luck in terms of the defenses he faced, consistently facing above average defenses over those two seasons. However, in the last six seasons Fitzpatrick's luck has turned with a vengeance. For six straight seasons Fitzpatrick has faced no better than average NFL defenses. The last two seasons have been particularly fortunate for Fitzpatrick, as he has faced in the aggregate the worst set of defenses of any starting quarterback in the NFL over those two seasons. When we factor in the easiest defenses faced in the NFL and the rather large upgrade in weapons for Fitzpatrick over the last two years, it is fairly likely that the recent surge in his level of play has little to do with actual improvement in his QB skills and much to do with a very fortunate set of circumstances. In short, it appears likely that the "good" Fitzpatrick of 2014 and 2015 is really not much different from the below average Fitzpatrick of earlier seasons, with the "improvement" likely attributable to easier defenses faced and better weapons. In particular, 2015, when adjusted for factors outside the scope of Fitzpatrick's skills, looks a lot less like a career year and a lot more like a typical, or even somewhat worse than typical Fitzpatrick year.
If, as many expect, Ryan Fitzpatrick ends up signing with the Jets in 2016, his adjusted statistics may provide some clues as to what we should expect from him going forward. With what looks, at least on paper, like a pretty substantial upgrade in terms of pass defenses he'll face in the upcoming 2016 season, a reasonable projection is that Fitzpatrick's statistics will regress fairly substantially in 2016. If you loved what you saw from Fitzpatrick in 2014 and 2015, it may make sense to keep in mind that those seasons may have been somewhat of a mirage. What you see going forward is more likely to resemble the pre2014 Fitzpatrick than the "career year" Fitzpatrick of the last two years.