Comment by Arech

My dog (Briard) isn't just addicted to play fetch with balls.. Since he knows that when another dog enters the dog park, the ball will be removed/hidden from him (to prevent the dogs clashing trying to get the ball), he becomes hostile to the dog entering the park, actively trying to prevent them from doing so! This happens only if we started to play with balls. If not, he'll be totally friendly... What an ass!