Dog aggression

my question is why is my nephew's pb aggressive to strangers (must be adult size though) when on the chain but off the chain she would just go and sniff the same stranger then wanna play fetch and get pet by that same stranger? She will not show any signs of aggression towards kids though even when she is on or off the chain.

 

Alot of dogs are territorial of their chain spots:cool:

 

i look at it like this if some stranger just walked into my house i would well make them leave but not be nice at all. If i met that same person out at a store or some place like that i wouldn't act the same way towards them

 

The dog is territory aggressive/chain brave

 

called Chain/Kennel Crazies.
Just territorial of their space like everyone said.

 

Thanks all for all your input!!