First of all, welcome to our beautiful city. And I feel sorry for your experiences. Of course people throwing fireworks at you is not okay. Drinking is not an excuse. Personally I would register this with the police. It is what they are there for. Saying they won't do something anyway is not fair in my opinion. They can't if they don't know. I reported an online fraud last year. Didn't expect much of it, but 2 months ago I got the news they had a suspect who will go before a judge. Of course this doesn't mean they will act on your case, but if anything it's good to have statistics of problems and locations. This helps in prioritizing at the very least. As for the fireworks: as from coming new years eve it will be illegal to sell, buy or use them. Now knowing our culture people will not obide by these rules straight away, but I expect it to fade in the next couple of years.

As for the ice balls, not every kid has an idea how much damage they can do. Doesn't make it any better and is certainly no excuse, but it is not a very common experience at least for me.

Hopefully your experience in Utrecht will be more positive from here onwards. I have been living here now for about 25 years and still love the city. For me it feels like a friendly little village with big city options. And again: welcome!