I caught the tale end of this - what actually happened was a man was arrested by a group of plain clothes police. It must have been a preplanned operation as the cars all sped in and stopped pretty much simultaneously around the corner of the road and they were all on him pretty quick. I can see how it might look they were beating a man on the floor at a glance, they were getting hand cuffs on him as he struggled. They were identifying themselves as police and some had caps on, they then started taking stuff from the bloke's pockets and bagging it up. That was the end of what I saw. I can imagine it might have been stressful for the boy, hopefully an explanation of what happened might help.