forum for week of Nov 7: kinds of apriori beliefs

I had a long debate with a previous metaphysics prof about whether rules of games could be considered a priori knowledge, ie. that three strikes constitute an out in baseball. This really just comes down in the end to how wide the semantic content of the term "baseball" is. Does the term "baseball" necessarily denote "the game in which three strikes constitutes an out", or is that instead non-essential data to the concept of baseball that must be obtained via experience.