beattie 819 - it is a myth that foxes kill for 'fun'.
Foxes kill for food like all wild predators. If there is one hen, the fox will kill it and take it away. If there are half a dozen, he will take one away, and come back for the rest which he will bury for future consumption. This often leads to the sight of dead hens left, and the fox nowhere to be seen - he will not return if there is fresh human scent near his kills.
Like all predators, foxes are opportunists - if they have a chance to kill more prey, they will take it, that is survival instinct, and the notion of some sort of sadism is a myth encouraged by country people who regard foxes as vermin.
Foxes are killers, but only for food, not for 'fun' - that is far to sophisticated a concept for an animal to understand. After all, how often do you hear fozes laughing as they run away?