The term BASEBALL ARBITER, FOR SHORT is an abbreviation for UMP, which stands for umpire. An umpire is an official in the sport of baseball who is responsible for making decisions on the field during a game. They are responsible for calling balls and strikes, as well as making other rulings such as fair or foul balls, safe or out calls, and other judgement calls. Umpires also enforce the rules of the game and ensure that all players abide by them.