I just witnessed something so crazy

Im an ambulance driver in central London so I see crazy shit all the time. But today i literally saw a man(a civilian) run out of a coffee shop and wrestle a man to the ground. I thought he was being mugged, until a 2nd civilian ran out after him holding a small knife, and it became apparent that the man he had been wrestling to the ground was about to stab someone. The man with the knife then got wrestled to the ground by around 6 civilians until the police arrived. People are crazy.