In Washington any report of domestic violence to which police respond, requires that an arrest be made regardless of circumstances. I knew of a case a few years ago where a husband and wife got in a shouting match and ran out to the street. A third party who was driving by called the police. There was apparently physical contact, but no allegation of hitting. Not even clear who initiated the contact. Police were required to arrest someone so the husband took the arrest. All charges eventually dropped but husband spent night in jail.
Key Phrase:
THERE WAS APPARENTLY PHYSICAL CONTACT AKA EVIDENCE AKA PROBABLE CAUSE.
If there is NO, ABSOLUTLY NO, NONE, evidence, probable cause the cops wont arrest anybody.
They will however, separate, make sure the situation, shouting match, etc, is either DIFFUSED, DESCALATED, AN OR GIVE ORDERS that they are to be separated.
Another example:
A roommate in Chewelah, went on a vacation. Somehow, I dont know how, but the roommates waterhose ended up tied, tangled up
I didnt do it. The roommate blamed me. And grabbed me, threw me on bed, proceeded to put his 78 year old knee, into either chest, neck, making it so that I either couldnt breathe, or hard to breath.
The proof that he did that, a mark that left, faded by the time the the cops got there, because they were called by his wife.
After listening to his wife's story, his story, my story, and seeing no physical evidence(faded, disappeared by time cops got there), the cops didnt arrest anybody, and gave separation orders, and since I did not have a car, ride, gave me a mandatory separation drive to someplace far enough away, ordered me not to go back, and that if I did go back, violated order, I would be arrested, if I did so.
I was lucky the crazy old man either didnt choke me to death, kill me, an or, since I was just about ready to punch him in face, give him a black eye, etc, if he hadnt stopped like he did, because if he hadnt stopped, and if I had hit, gave the old man a black eye, even in self defense, I would have been arrested, and likely convicted, because nobody would have believed me over the crazy old man and his wife.
That happen in 2011. So unless the law has changed between 2011, and now, the law is, that the cops wont arrest anybody for 4th degree assault domestic violence, unless there is evidence, PROBABLE CAUSE.
So that either applies, should apply to Mark's case, that the cops wouldnt have arrested Mark for 4th degree assault domestic violence unless the cops had probable cause, evidence.