You call the police and let them deal with it. You don't chase someone down and shoot them multiple times for something, ANYTHING, they did (and are no longer doing) Even if he tried run the biker off the road, that doesn't justify pursing the fleeing truck and shooting him. Exceptions, of course, are thing like the truck driver kidnapped a family member and is holding them in the truck etc, a felony crime that he is still committing. In the eyes of the law a confrontation is over once one party leaves and creates a separation of time and/or distance. If the other party follows then that the resulting NEW confrontation is on the follower. At the most basic level the purpose of self defense laws are to keep you alive - more specifically to accept that the natural human instinct is to preserve one's own life (or the life of an innocent), and to forgive those acts carried out under this instinct that would otherwise be punished. Once the threat to your life is gone, the person runs/drives away, then THAT IS IT. Self defense laws no longer apply. You are not a cop, you have no duty to pursue and apprehend. You have no business trying to apprehend. That why we have police officers. Drop a dime and stay out of it.