Originally posted on Buffalo Wins  |  Last updated 5/28/13
Last time, we examined about how much safeties, namely Jairus Byrd, should make based on their historical production. In this post, I’d like to forecast Byrd’s future play based on his age so we can then apply the polynomial regression determined last time to his expected production in order to find annual salaries Byrd should receive. To get an overview of how safeties age, I first compiled a list of the top fifty safeties for the past six seasons, based on their EPA+. 78% of the 300 players were under 30, and only 3% of the players were over 35. The distribution of the players by age is in the graph below. The drop off after age 27 is pretty staggering, but it makes sense. The top fifty safeties each season make up 78% of the 64 starting safeties in the NFL and any player below that fiftieth ranking could be considered replacement level. Once a player slips below that level, they can be replaced by a younger player. In order to determine an aging curve for safeties, I plotted the maximum performance for each age over the past six seasons. I limited the age range to be from 22 to 33 because those age groups had at least five data points each. From that data, I only need to correct one data point: Ed Reed’s 30 year old season in 2008. He was ridiculously good that season and I determined his 2008 performance was an outlier for any aged safety. Interestingly enough, the distribution resembled a parabolic shape, which is logical. As a player gets more experience and playing time, he gets better until his body starts to break down or he loses a step. That loss in ability happens quickly, as depicted by the age distribution above. The safety aging curve, as measured by maximum performance is in the graph below with a polynomial trend line (black line) and the Ed Reed outlier (in red) is below. The graph and trend line above compared maximum performances for each age group, which is independent of any one player. Because of that, it resembles the greater population with relative accuracy. The trend line predicts a player to have his peak season when he is 26, which matches our age distribution for the top 300 players. Byrd was 26 last season. In fact, his 26 year old performance was the best of any other 26 year old safety in the last six seasons. What can we expect him to do next season? How quickly will his play diminish? Because the trend line estimates maximum value for each age group, I converted the expected maximum EPA+ values into percentages of the largest value (the regression’s total when age is 26). The table below breaks down the expected EPA+ percentages of a player’s 26 year old season, by age. Age % of Age 26 Season 23 97% 24 99% 25 100% 26 100% 27 99% 28 97% 29 95% 30 91% 31 86% 32 81% 33 74% Once I applied the percentages above to Byrd’s 2012 season, I was able to estimate his production until he is 33 (2019 season). The graph below shows his historical production (red) and his expected future production (blue), again measured by EPA+. Based on the curve, we can expect Byrd to be better than his 2011 self until he is 32. He wouldn’t slip below a top-25 safety (assuming the average for top-25 safeties average above 30 EPA+ per season) until after his 33 year old season. Byrd could be a productive contributor to the Bills for at least seven more seasons. Based on the average EPA+ salary formula determined in the last post, I calculated the salaries based on Byrd’s projected performance for the next seven seasons. The results are in the table below. Season Age Byrd Exp EPA+ Annual Salary 2013 27 46 \$7,142,363 2014 28 45 \$6,914,957 2015 29 44 \$6,569,978 2016 30 42 \$6,118,001 2017 31 40 \$5,573,360 2018 32 37 \$4,954,164 2019 33 34 \$4,282,276 Based on those annual salaries, a five year contract should cost the Bills somewhere around \$32 million. His value for the next two seasons is around a total of \$14 million. Notice how his expected annual salary for next season is greater than the franchise tag’s \$6.916 million salary. Should they sign Byrd for five years? Seven? How long should Byrd want to be under contract himself? We’ll investigate contract terms in the next post in this series.
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