The Sophomore Slump in the NFL

Whenever an NFL rookie has a remarkable first year, their sophomore campaign often seems to not measure up, and the player is labeled as going through the dreaded "sophomore slump". Sometimes this decline appears to foreshadow future problems (see: Robert Griffin III) and other times it isn't anything but a blip in a long-term successful career (see: Matt Ryan). 

There have been two notable cases of it this year: Jameis Winston and Marcus Mariota. Winston was selected to the Pro Bowl last year, and Mariota had a solid rookie year as well. However, both players have regressed in Year 2. Why do some players take a step back in their second year? Shouldn't they improve as they gain more pro experience?

I pulled the numbers on the notable "sophomore slumps" in the past 10 seasons, sticking to QBs only. Limiting myself to QBs allows me to use "QB Rating" to quantify their performance in each year (and more imporantly, compare each player to the average for that year).

Player	Team	Year	QB Rating Year 1	QB Rating Year 2	Difference
Jameis Winston	TB	2016	84.2	75.9	-8.3
Marcus Mariota	TEN	2016	91.5	88.3	-3.2
Robert Griffin III	WAS	2013	102.4	82.2	-20.2
Sam Bradford	STL	2011	76.5	70.5	-6
Matt Ryan	ATL	2009	87.7	80.9	-6.8
				Average	-8.9

On average, these QBs' rating fell almost 9 points from Year 1 to Year 2. What if we compare each player's performance to the average QB rating in each year?

Player	Team	Year	QB Rating Year 1	QB Rating Year 2	Difference	vs Avg Year 1	vs Avg Year 2
Jameis Winston	TB	2016	84.2	75.9	-8.3	-6.8	-10.9
Marcus Mariota	TEN	2016	91.5	88.3	-3.2	0.5	1.5
Robert Griffin III	WAS	2013	102.4	82.2	-20.2	16.5	-5.2
Sam Bradford	STL	2011	76.5	70.5	-6	-9.7	-13.6
Matt Ryan	ATL	2009	87.7	80.9	-6.8	3.8	-2.5
				Average	-8.9	0.9	-6.1

These rookies were slightly above average in their first year, but do indeed check in well below average in their second year. This would seem to imply there is indeed regression and the "sophmore slump" is real! BUT...

Player	Team	Year	QB Rating Year 1	QB Rating Year 2	Difference	vs Rookie Avg Year 1	vs 2nd Year Avg Year 2
Jameis Winston	TB	2016	84.2	75.9	-8.3	7.5	-4.5
Marcus Mariota	TEN	2016	91.5	88.3	-3.2	14.8	7.9
Robert Griffin III	WAS	2013	102.4	82.2	-20.2	25.7	1.8
Sam Bradford	STL	2011	76.5	70.5	-6	-0.2	-9.9
Matt Ryan	ATL	2009	87.7	80.9	-6.8	11.0	0.5
				Average	-8.9	11.7	-0.8

The key word here is regression. Regression to the mean. In Year 1, this set of QBs was almost 12 points above the rookie average, but in Year 2, they simply regressed to the mean (almost literally, to less than 1 point below the 2nd Year average). This "sophmore slump" is real in the sense of declining year-over-year, but is simply another way of describing regression to the mean.