The "jock tax" refers to a type of income tax that is imposed by states or cities on athletes that make money while playing inside of a specific state or city. While the tax can also be applied to other businesses, it has been often used to charge visiting athletes since it is easier to track when and where they made their money.
These athletes are easy to tax because their income and their whereabouts on game day, which is a work day for them, is such public knowledge. For example, in the Super Bowl game that took place on February 1, 2015, the Seattle Seahawks and the New England Patriots played a highly lucrative game in Arizona, and the state of Arizona was able to collect money according to their "jock tax." The revenue from this type of tax occasionally gets re-invested in sports facilities. In 2015, Wisconsin Governor Scott Walker announced that a proposed arena for the Milwaukee Bucks would be at least partially paid for with jock tax revenue, giving professional athletes another place to play.