Alejandro Garza is 11 years old and is in serious condition with bites to his neck and legs.
Animal Care and Control officers now have the dog.
He was playing near the car dealership where his mother works when the dog attacked.
Elvia Garza says the dog was not provoked.
"It's a dog trained to kill, and I think the owner should be responsible. First of all, you shouldn't have it. Second, it shouldn't have been let loose," Alejandro's mother said.
She says a man working for a cable company used a hammer to get the dog off the boy.
The boy's expected to make a full recovery.