QUOTE (Jake @ Aug 8, 2008 -> 09:38 AM)
What I thought of here was on 9/11 when the passengers of one of the planes stopped the terrorists from crashing it into whatever building they were aiming for. I think a lot people, at least Americans, would band together against someone doing such a terrible deed even if some damage had already been done. (Who's to say he wouldn't go after someone else with that knife?)
If he was say, trying to go after the driver while the bus was moving, then of course you have to try to stop him.
The first rule for any responder is to make sure you don't become a victim yourself, because all that does is make it harder on everyone. More EMT's required, more blood spilled, more risk.
If a person is having a genuine psychologic episode that you can't deal with, and he's not putting anyone else in danger, the rule is to back off and wait for more advanced personnel. The only reason to violate that rule is if he's legitimately putting other people in danger with his behavior.