An announcer at a ball is commonly referred to as a "master of ceremonies" or "MC." This individual is responsible for introducing performers, guiding the event's flow, and engaging the audience. In some contexts, especially in formal dances or balls, they may also be called a "caller," particularly if they are leading social dances.
Havlicek
These people are called the "announcer"
The announcer
A herald.
When Babe Ruth the ball out of the park the announcer screamed "Holy Mackerel!"
They were called heralds.
A Nascar annoucer is called a commentator.
A court announcer is typically referred to as a court crier. They are responsible for making announcements in the courtroom and maintaining order.
Ringmaster, ringleader or Equestrian Director
a hemisphere.
It is called a "ball"
When a ball has scored its last hoop point, it becomes a rover.