no seriously.....a wanna be cop would need a death wish
enforce the law?......by hand?
Not really. The force could be brought on-site in case of escalation. And the terms would be that once that force was put in play, all bets are off. If they had to call in "SWAT" for example, then the public persons involved would know they were on their own, and again - as stated on the website linked, the public would need to be on board with this. If it got to a point where the use of force were approved by some authority - the police chief for example - then that escalation means that certain risks to perpetrators safety are necessarily in play.
So, your best bet would be to deal with the cops in front of you - otherwise you bring a crap-storm on yourself. And the police would need to function somewhat differently, obviously - such that officers were always in pairs at the very least, and in situations suspected of requiring escalation, you'd ideally send two cars of police, such that someone could always call-in the escalation request if necessary.
In the U.S. I admit it would take quite a while for the public to get used to the idea and how it functioned... and at first it would be a hard sell, and we would possibly see people taking advantage of what they know is an unarmed front-line for a time. I honestly don't know if the U.S. is beyond the point of hope on this point. Could be, I suppose.