I used to have a couple of neighbors (men) who lived beside each other in the duplex next door. One night they got into a nasty fight and one of them ended up in the hospital. The other one was clearly the aggressor according to eyeitness accounts, but I was later informed by a detective that unless an officer witnesses an assault he cannot arrest anyone.
Just an FYI for your husband.
Next time this happens, dial 911 but don’t say anything. Just dial and then put the handset on the counter or table or floor. If the 911 operator isn’t able to interact with the caller but can hear commotion in the background, s/he will assume there’s an incident in progress and the police will be dispatched with great urgency. It’ll be even better if you can do this out of sight of the front door, because it takes just a moment, and the guy won’t realize you’ve called the cops. It will be exceedingly satisfying to have the men in uniform suddenly appear and tackle the jackhole off your porch. 