Would it be "legal" to kill a dog if one was attacked by one in the street, if that dog was unleashed, presumably feral, perhaps with rabies, and obviously biting and aggressive?

I ask because there are some scumbags up the street that let their nasty poodle-mix mutt out of their house to run around. I was walking my dog Ellie when the dog more or less attacked us.

I presume it would be more legally appropriate to do something like call the police.

Thoughts?