A story on Stateline.org reports solid revenues from a somewhat unlikely source: visiting sports teams.

Known more familiarly as the “Jock Tax,” Pennsylvania and New Jersey tax the income of visiting athletes. According to the Philadelphia Inquirer, Pennsylvania alone collected $18.6 million in 2008 from the state’s seven major-league football, baseball, hockey and basketball teams. This amount includes taxes levied on visitors’ salaries.

“While the concept of the jock tax is simple, calculating the right amount can be tricky,” reports the article on Stateline.org. “Visiting athletes are taxed for each ‘duty day’ spent in the state, defined by the city of Philadelphia as any day ‘on which (an athlete) participated in a game, practice or workout in Philadelphia.’”

For example, the New York Yankees were charged for five duty days for the three World Series games at Citizens Bank Park.

California was actually the first jurisdiction to tax visiting athletes.