Answer: The association is due to confounding (major league teams tend to be in large cities with more people, hence a greater number of divorces.)
Explanation: In research statistics there's a concept called confounding which is essentialy a variable that influences both indepent and dependent variables.
In this particular case, what really influences that prevalence of divorce is not the fact whether there are major league teams in a city or not, but the fact that major league teams tend to be in larger cities with more people, therefore the number of divorces is higher.