"Breed-specific legislation (BSL) is a law that bans OR restricts certain types of dogs based on their appearance, usually because they are perceived as “dangerous” breeds or types of dogs" - https://stopbsl.org/bsloverview/
The purpose of breed specific laws is to limit the number of bites and attacks against humans and other animals in the United States. Unfortunately these laws barely solve the problems, instead they create a lot of confusion and misunderstanding.
The law uses dog bite data to determine which breeds are dangerous, therefore should be banned. Banned breeds that can fall under this category (American Pit Bull Terriers, American Staffordshire Terriers, American Bulldogs, Rottweilers, Mastiffs, Dobermans, etc.). Decisions are made by external appearance like square head, short snout and broad chest. The problem is, that without a DNA test, it's often hard to define the breed of a dog. On top of that, there are a lot of mixed breeds which makes it even harder to have a clear legislation.
Breed discrimination is not only ineffective, but also expensive and hurtful.
Countless entirely perfect dogs end up losing their lives in shelters, because they are not allowed to be adopted in certain cities or counties. BSL makes it harder for dog owners to find housing, since many landlords will not allow these breeds, or they require an extra fee. Some owners choose not to give up their pet due to breed restriction, so they have to hide their dog, forgo proper vet care, spaying and neutering, microchipping and vaccination. Limiting the dog's exposure to outside activities can also lead to health and mental issues.
If you are interested to see whether your city bans certain breeds please refer to this map.