There are many different Rule Sets in the game of baseball. The focus here will be High School and NCAA Rules, with an occasional mention of other rules for specific leagues. 

Rules basically all the same or similar, but contain minor tweaks for specific leagues. The most common set of rules that people refer to is MLB, more commonly known as OBR, or Official Baseball Rules. 

Umpires will constantly study rules and their differences to stay on top of the game. Happy Learning!