Citizen's implementation aside, I feel like there's a real market for something like this. I was walking down the street a few months ago and was physically attacked by somebody (as in, the man punched and attacked me until I ran out into the middle of the street into oncoming traffic for safety).

I feel like there should be some sort of service that's able to offer some kind of protection in situations like this, or at least able to track down and prevent this kind of person from recommitting after he's shown a willingness to violently attack other people.