When ESPN asked us to write a piece on the development of the Jets' passing game this season (which you will find here), it got me thinking of the question of when quarterbacks develop the most.
A few years ago, when he first came up with the Lewin Career Forecast, David Lewin look at our numbers for quarterbacks and found that quarterbacks improved the most between years 1-2 and years 3-4. I've quoted that research a few times over the last couple of years, and I wanted to give Sean McCormick those numbers for the ESPN piece. The problem is that David Lewin did that research back when we only had DVOA numbers for six or seven years of quarterbacks. Now we have 21 years of quarterbacks, so I went to go try to duplicate the research in order to make sure I got the same results.
First, I looked only at quarterbacks who threw at least 100 passes in two straight seasons. I grouped them by experience, then averaged their rise and fall in DVOA between the two seasons. The results were pretty dramatic. The average quarterback who has at least 100 passes in both his first and second seasons will improve by 12.8% DVOA in the second year. But every other year, the average change varies between around -5.5% and +3.5%, and variation looks like it is just noise. although it might be interesting that two of the bigger year-to-year drops happen in years 9 and 11, which is roughly around ages 30-32.
Of course, looking at change by looking at seasons with at least 100 passes will leave out a lot of important players -- the ones who decline so much that they can't get jobs anymore. So next, I looked at DYAR instead of DVOA, and looked at the change for every quarterback from one year to the next. Any time a quarterback played in one year but didn't play the next season, he got 0 DYAR for that second season. However, I did not count quarterbacks who were below replacement level in one year and then didn't play the next year. Otherwise, we would end up assuming that terrible quarterbacks get better when they don't play. That's different from assuming that a 30-year-old quarterback who drops out of the league (or becomes a backup who never sees the field) probably doesn't throw passes because he's dropped to replacement level (or below).
Once again, looking at things in this fashion made the transition from year one to year two stand out. Quarterbacks gained an average of 136 DYAR between those two seasons. The changes between years three and seven were close to zero. Around year eight, or roughly age 30, quarterbacks began to lose more and more DYAR each season, a lot of them from dropping out of the league altogether rather than playing both seasons but declining from one year to the next.
Overall, I would say these two views of quarterback development suggest that the only year when quarterback improvement is significantly likely is year two. Then you have a few years where guys might improve or decline unpredictibly. There isn't really anything special about the fourth season. And then around age 30 or 31, as we've seen in previous studies, quarterbacks begin to decline.