It really really depends.
If I believe there is imminent danger, I will always move to action.
There is only one instance I ever called the police and it was a suspicious dude offering this thing (can't really describe it) to people and telling them to come closer and was being incredibly aggresive.
If you neighbourhood is a gang neighbourhood, chances are the cops know and they can't do **** all about it.
Shots fired. You better ****ing believe I'm callin the cops, but I if I can hear those shots from the 31st floor... there's others calling that's for sure.
Neighbour beating his wife... well. That's always a toughie to get involved in, but If I had seen sufficient proof, visually that it was happening, you better believe I'm telling the authorities about it.
Beating a child. ****, I'd find it difficult to not walk in their and beat the parent down myself. That **** ain't right. But there's a difference, I was spanked and I turned out ok... mostly
All I have to say atm.