Inside baseball describes technical matters only of interest to specialists or enthusiast rather than the casual observer.
Baseball references are commonplace general English: a politician hits a home run or strikes out (while Californian criminals famously have three strikes or convictions before they get a mandatory life sentence). He/She is also wary of curve balls or attacks from unexpected directions.
Where does the word baseball come from?
What is a curved ball?
The Language of Baseball: A Complete Dictionary of The Grand Ole Game