Throwing full size cobble stones at police should be met with return fire. That’s attempted murder.
I think it is easy to determine where violent action is taking place, fly the helicopter a few feet over the buildings and notify people deadly force will be used in this area, and then start shooting. If you want to be squishy, you could start live fire with rubber bullets.
Then again, I've been where police started shooting pepper balls and rubber bullets without any warning; I was standing three feet away from the cameraman who took a shot to his camera lens covering the DNC freakshow in Los Angeles in 2000.