Yeah coz that'd be a great thing to do wouldn't it you dumb f**k, its not the dogs fault the fence is insecure, if my dog had done that and you kicked him i'd beat the living shite out of you.
Knock on the house and tell them whats happened and that your taking the dog to the vets and see if their gonna help with finance. If they get arsey kick the owner in the eye , hope your dogs ok.
It is the dogs fault, why would it need to bite the dog?
Protecting it's own I'd say or just plain naturally aggressive, or maybe the dog has been teased by some folk passing, who knows really,