What is a dog called in a dog fight?

Answer 1

Abused and exploited in my opinion.

But, to answer your real question, they usually would refer to them as "game dogs". Other dogs used in "training" are called "bait dogs", because they are used to bait the fighting dog and are often mauled and killed in the process.

Individual dogs are usually either called by name or by gender. When referring to them by gender, they would call the female a "bitch" and the male a "dog". Often that could also have additional information, like color, e.g., "black dog" or "brindle bitch." Or, they might be referred to as their breed, such as "the white bull terrier bitch" or "the black pit bull dog."

Answer 2

It is called 'dog fighting' and it is illegal in the US and other countries. It is also cruel and vicious. Dogs are sometimes allowed to fight to the death, and dogs who are forced to do this can be very badly treated outside of the fighting venue as well. Often, such dogs are not able to be rehabilitated after rescue and must be put down. To treat animals who are so willing and able to share life with and to be faithful to their human caregivers is unconscionable.