The passengers, where fit and able, have a duty of care to ensure their own and other pax's and cabin attendants protection. The pointy end crew should never have to get involved. other than to radio for police to meet the aircraft on arrival.
I have never had to intervene in a situation on-board an aircraft (Canadians seem to be more civilized then some). However, once, on a bus a woman driver let a low life on-board without paying the fare and said, "Alright, I'll take you across the bridge". Across the bridge he did not get up and get off so she told him to get off. He came roaring up the bus and as he got to the driver his right arm was outstretched, fist clenched. I was sitting right there and grabbed his right wrist and the scruff of his neck. She told him to get off again. He made no indication of doing so so I literally lifted him up and put him on second step down with a push towards the pavement. She later said thank you. I said,"You take care on here".