Just one instance of many of the underlying complexities.
- We have a police force that expects certain classes of citizens to be extremely problematic, and so they are on edge, easily angered, and prone to making errors of judgement (especially after 2 or 3 back to back shifts).
- We have a citizenry that expects cops to be on edge, easily angered, and error-prone, and who are accordingly defensive and problematic in their interactions with police.
Until one or the other side can manage to stand down, this problem isn't going anywhere. Police can be, and are, trained to (essentially) stand down. The term we're using these days is "de-escalation", but there's pretty broad understanding on all sides that they're not trained very much in this.
(and, of course, we have a media that delights in whipping up the problems and making them seem as bad as possible which, given that the problems are largely problems of perception, actually worsens the situation - police successfully arrest poor petty criminals every day without shooting them or beating them to death, and citizens, even poor ones, have pleasant well-mannered and productive interactions with police every day, but you certainly wouldn't know it.)