How to stop police brutality? Comply with the officers orders. Communicate with the officer as if the officer is a real person.

If someone has gone of their meds, or is having some mental health issue, call a mental health professional to deal with the situation. They will come out, for free I'm sure, and gently calm the person down. You don't call a cop if someone breaks a leg, why call a cop for a mental health problem? They are not mental health professionals.

I don't think this was a rally against police brutality. It appears from the second photo that it was a rally against police.
That one sign said, "Cops, pigs, murderers."