its usually the owner....but that being said certain breeds do have tendencies...if you arent a good dog owner...you have no business owning a medium sized dog
a german shephard will tear through most other dogs in seconds
hell i watched mine as a kid rip the shit out of two mid sized terriers/bulldogs after they bit my sister.
ill even tell the story.....i was walking up my hill toward my sister, the dog was at the bottom, tied up with a chain we though she could never break...lol
anyway the dogs were owned by some people who came up each summer, and the dogs were vicious they had attacked me but i was on my bike and just drove away.
anyway that day i was halfway up the hill when they attacked my sister, she screamed a real scream that brought Bo(our dog) out of her house and running full speed. the chain snapped like it wasnt even there...it was a big ass chain as well...anyway i started to run up the hill...Bo passed me after maybe 8 seconds...and i got to the top of the hill just in time to see the two dogs starting to realise they had fucked up big...lol
she just ran full speed into the first one and chest butted it..sent it flying (bo was over 100 lbs) then she stopped on a dime turned and picked the other one up by the rib cage, she just sank her teeth in..and started shaking and pushed it to the ground...then she turned on the other who was already running away....she didnt chase it though..she went and just sat down beside my sister
i miss that dog