So there is data on some policing in NYC. Because the police need to record stop and frisk encounters, it turns out that black populations get stopped and searched at 2-3 times the rate that other racial groups get stopped and frisked (whites got 10% of the encounters despite being something like 33% of the pop and black+latinos got 90% of the encounters). And it's not like the frisks turned up anything, with the vast majority (90%) of the frisks finding nothing. I believe there's similar data for police in other cities.

At the very least, this suggests that police in NYC and probably elsewhere were disproportionately singling out Black (and Latinos) for intrusive searches without evidence and on a pretextual basis.