I hear you, but the Knockout game officially involves surprise, by its nature. The weapons are fists, and the attack generally comes from a kid or teen that breaks away from a group of kids at short range from the victim, and sometimes from side or behind. It can be spontaneous, so even the other members of the group don't know beforehand that an attack will happen.Draw before the threat becomes a strike.
So, unless the group shows warning signs, you'd have to draw on every group of kids that looked a bit suspicious. I don't see that being feasible.
But about vigilance and awareness, I agree. Be careful about roaming groups of certain types of kids, keep distance from rowdy groups, and be ready if they launch an attack!