Q: The White Sox are really good at the fundamentals of baseball. Which is why they won the World Series in 2005.

A: The White Sox are really good at the fundamentals of baseball; which is why they won the World Series in 2005.

Is this correct?

3 answers

No. Your clause after the semicolon is a dependent clause, not an independent clause. It cannot stand alone.
So I need to write

The White Sox are a really good at the fundamentals of baseball, which is why they won the World Series in 2005.
Yes.