A lot has been posted about the ambiguity of the protests by various NFL players. There are many different answers to the question "what are they protesting", but most can be categorized as racial inequality. I began to read more about this topic after the highly publicized deaths of black men at the hands of police. I was less interested in assigning blame for those particular events (they are certainly not monolithic) than I was at understanding the reaction to these events. I'm not just talking about the reaction of the typical leftists crap stirrers on cable news...as they are as inflammatory and biased as the typical right-wing crap stirrers. I had dear friends that were deeply hurt and concerned. I had friends who had adopted children of different races that incredibly disheartened and even scared about the prospects of their black child having to grow-up where he mighty be penalized for the color of his skin.
Anyway, that all led me to look into the topic here. I think you get a better view of someone's argument when you let them make it. . .as opposed to letting someone who disagrees summarize it. Our culture prefers a "safe summary" to actually engaging in the argument presented by the opposing side.
All that said, the link shared below seems clearly biased, but it also seems to be true to the academic sociological understanding of the issue. I don't agree with all the conclusions or premises, but if you want to understand why there is such an uproar in the black community, I think this may be a helpful thing to read. Again, not to convince you that their argument is right, but so that you will understand what their argument is.
https://www.thoughtco.com/systemic-racism-3026565