In July I blogged about MLS income inequality and one reader asked me about the NFL. My response, was basically - cool idea; I don't know; have not done it. Now I have. I am using the Gini coefficient (step-by-step guide to make this calculation) which is a measure of income inequality. The Gini coefficient is bound between zero (complete equality) and one (complete inequality). For comparison purposes, the Gini coefficient for the US in 2010 is 0.411 (or 41.1 for the Gini Index, which is the Gini coefficient multiplied by 100).
Specifically, what I have done is taken every active player pay (not the amount attributed to the salary cap) listed on the website for the 2014 season and measured the amount of income inequality. I have not included players on injured reserve or players that were given a contract but then dropped from the team. Here is the link for Arizona in 2014, follow the dropdown menu for the other teams. Once all the players have been included in the dataset, I have a total of 1688 NFL players in 2014. Total payroll among those players was $3.331 billion. For all the active players, the Gini coefficient was 0.5942, which is quite a bit more unequal than the US in 2010.
UPDATE: (09/16/2015: US Gini coefficient for 2014 is 0.480.)