Would you intervene in and Anti-social behaviour incident, or vandalism, or an assault?
Apparently a YouGov poll says that 2/3 of us would walk on by.
There was a time when if I saw two or three ganging up on someone I would wade in and to hell with it. I wouldn't do it today, even if I was younger and fitter. I certainly would not do it for vandalism; and I have become so immune from anti-socail behaviour I couldn't care less.
The very most I would do nowadays is phone the police and wait to see if they turned up.