My ex and our children have lived in a three family (side by side and one above) house for nearly two years, without having any issues whatsoever with neighbors complaining about any noise. The neighbors next store moved recently and a couple and their 9 year old son moved in. In the roughly two months they've lived there, the husband/father has pounded on the walls and angrily screamed "f'n" this and that at least half a dozen times because he felt our kids were being too loud. The pounding on the walls isn't just a "hey, turn it down" sound...it's BOOM BOOM BOOM so loud and hard that it shakes the wall, and along with his screaming, is quite threatening and intimidating, and scaring my children. It honestly sounds like he's losing it on the other side of the wall. His first introduction to us was coming to the door and screaming at my teenage son. We tried talking to him but he immediately got defensive and said "this conversation is over" and that was it. Although he agreed to ask for my ex if/when he has an issue with noise, he's since had another two or three angry outbursts, pounding on the wall and stomping up and down his stairs. The landlord isn't too sympathetic, and although I don't live there, feel I need to address it now without getting in a confrontation that could get ugly...the guy is volatile. My question is whether or not contacting the police the next time he explodes is an appropriate next step...or should we talk to the police now before it happens again? If they do come to the house and talk to him what sort of charges would be brought if he were to do it again?
It should be noted that the level of noise my kids make is consistent with any other family...in fact, they are often walking on egg shells because of this guy, which is a pretty stressful existence for them.
Thank you for any advice you can offer.

Volatile neighbor
This is a very common situation that, unfortunately, I do not have a great solution for. You can read this post in which I advise another person with similar problems to contact the police and the landlord about the noisy neighbor. However, the response you get is likely to vary greatly from one police officer to another and from one landlord to another. Certainly, if the neighbor is engaging in threatening and unacceptable behavior, your landlord has an obligation to talk to him and help protect your quiet enjoyment of the unit. But I'm sure you can predict how that will go: Your neighbor will claim YOU are interfering with HIS quite enjoyment. At a minimum, I would think that if a police officer talked to him, your neighbor would have enough sense to cease the pounding on the wall. Sorry I can't offer more help, but these situations are extremely difficult to solve (short of one party moving).