Recounting the incident to the Advertiser, another neighbour, Anthony Dear, said the dog just “snapped”.
Mr Walker added: “He wasn’t aggressive or anything. I don’t know why it snapped down there.”
A spokesman for the City of Port Adelaide Enfield Council said: “The owner surrendered the dog, and it was immediately removed from the property.”
The dog is currently being held in kennels as the authorities investigate the incident.
South African Boerboel Mastiffs are normally used as family guard dogs. Fully grown males can weigh between 68 and 91kg.