Please take a look at the linked article (and HN comments https://news.ycombinator.com/item?id=23385741) and note that the Federal "Kerner Commission, which was formed in 1967 to specifically investigate urban riots, found that police action was pivotal in starting half of the 24 riots the commission studied in detail."
Today we can see ample evidence of police escalating use-of-force (rubber bullets, tear gas, batons, etc.) on peaceful protesters.