As a retired teacher and a trained foster parent, I am mandated to report abuse. If it's an adult abusing a child, I will try to speak to the adult (gently) tell them who I am and what my responsibility is. I might try to defuse by saying something like, "Uh-oh, somebody's upset," to see if it might deflect the abuser and get them to talk to me, even if it's in anger. If all else fails, then I make it obvious that I'm going to film them.

I guess I'm a busybody. I can't stand seeing anyone bullied, so I always intervene, even though I know I may be taking a risk for my own safety. I notice that teachers and ex-teachers seem to intervene more than do others. The victim is usually grateful for your support.