Seeking causal effects from a rule change. How did changing the “roughing the passer rule” in 2018 affect salaries for quarterbacks in the NFL?

Following concerns for players safety, the National Football League (NFL) chose to protect the quarterbacks (QB) further by changing the “roughing the passer rule” in 2018. This paper studies the effect this rule change had on QB salaries. This is done by applying a Difference-in-Differences approach on salary data stretching from 2013 to 2021. Our estimate show how the salary increase following the rule change around 900 thousand dollars when excluding bonuses, while the actual increase reach 1.2 million dollars. Considering the wages for the top 30 percent of QBs, we find an increase of actual spending approximately reaching 3 million dollars, while for the top five percent the increase of actual spending lies at around 1.3 million dollars. Controlling for time trends gave us answer similar to our original DID approach, but our robustness checks gave us treatment effects similar to the ones from our DID approach. We conclude that since there are treatment effects, even when there are no treatment, we cannot accurately state that it is the rule change that creates the treatment effect