When i lived in portland Or you could call animal control. They would speak to the person and eventually fine them if necessary. You would need to know the dogs address and it would help to film it with your phone. Portland is a bigger city and had clear leash laws.
An "aggressive" (or distressed) animal is usually a sign of a neglectful or abusive human harboring them: if anything, have compassion for the animal, and get the animal help - that is the most emotionally-intelligent thing that you could do in that situation. PETA CID has a good 24 hour unit if no one answers you locally: you can Google PETA's CID unit contact information online, and they certainly do care about animals.
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