But just because there’s no data about protests that can be easily compared in a chart doesn’t mean we’re bereft of information, said Pat Gillham, a professor of sociology at Western Washington University. There’s 50 years of research on violence at protests, dating back to the three federal commissions formed between 1967 and 1970. All three concluded that when police escalate force—using weapons, tear gas, mass arrests and other tools to make protesters do what the police want—those efforts can often go wrong, creating the very violence that force was meant to prevent. For example, the 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. It recommended that police eliminate “abrasive policing tactics” and that cities establish fair ways to address complaints against police.