I hear ya man, it's a bummer you have to deal with this too in your personal life...but the guy here is a clear danger to society, just based on those arrests for assault the court should order him a mandatory psychiatric stay at an institution.The problem is, mental health in the U.S. is a joke. Most times someone like him can be taken in and institutionalized for observation to determine if they are a threat to themselves or others. This usually lasts less than 2 weeks and if you know how to play the system and give the right answers, they will cut you loose, especially if you have no insurance for long term commitments to get real help.
What they'll do is start the patient on meds to alter their behavior, basically making them docile walking zombies and recommend they continue seeking mental health help once released, but there are no court orders to do so and the patient, upon release, can just go back to what was normal before being sent in for observation.
I've got a 29 yr. old step-daughter who has been diagnosed as "Schizoaffective" and she is currently on 8 different medications a day to control, or lessen her issues. If she quits taking her medication, within a few days she is showing signs of reverting to being off the charts with her behavior. She is living with the wife and I and I made it a mandatory requirement for her to continue taking her meds for us to give her a chance to get her life in order. If she chooses to quit the meds, she needs to find someone else to put up with the fallout of her decision. With meds, she can function in society, without meds, she's a total whack job with no chance of a future.
If he is going around punching random people on the street, it's possible he is imagining they are boxers, he maybe having hallucinations thinking all of this is real. Imagine he thinks of himself as a racecar driver next and mowes people down on a sidewalk. It will be too late then to think about intervention.