What amount of physical force, if any, can be used to prevent animal abuse (a dog's owner hitting the dog, with a minor present) in Oregon? Is it legal to restrain the owner? Take the dog to a safe area?
If someone attacks your dog, or the dog of a third person, you may use force to defend property rights, see ORS 161.205 and ORS 161.229. This does not apply to a person attacking their own animal. Force may also be used to effect an arrest by a private person (ORS 133.225) – you "may arrest another person for any crime committed in the presence of the private person if the private person has probable cause to believe the arrested person committed the crime". You would need to study up on ORS 167.320. Assuming that the abuse is less than causing death, for first degree animal abuse, it is when one "causes serious physical injury to an animal". The child actually becomes relevant because the misdemeanor becomes a felony when
The person knowingly commits the animal abuse in the immediate presence of a minor child. For purposes of this paragraph, a minor child is in the immediate presence of animal abuse if the abuse is seen or directly perceived in any other manner by the minor child.
So in fact, no amount of force can legally be used to prevent a person from hitting their dog. Force can be used to arrest a person (which prevents any further beating), if the person causes serious physical injury to the dog.