> This is an interesting conclusion, because as I understand it this is only really true in some states. Wisconsin's self defense law is more permissive than many, and so Rittenhouse probably couldn't have used the same defense as easily in many states.
Let's look at the five rules of self defense as they apply pretty much everywhere in the US. The last one is the big difference in Wisconsin.
* Innocence (was he there to commit a crime or hurt someone) -- Rittenhouse was generally there to help people. The altercation was started because he put out a fire.
* Imminence (was the use of force against him about to be used) -- The video shows Rosenbaum cornering him and lunging. The gunpowder stippling pattern shows that Rosenbaum's hand was on the barrel of the gun too. He shot at Maurice Freedman (jump kick man -- his identity was known to the prosecutors, but they hid his identity) who was in the process of trying to kick his face in with heavy boots. He shot at a guy assaulting him with a skateboard. Finally, he shot someone pointing a gun at his face.
* Proportionality (not excessive force -- in this case, only deadly force can be stopped by deadly force). I don't know of any state where grabbing a gun, pointing a gun, hitting someone with a skateboard (they weigh around 11 pounds -- a baseball bat weights around 2 pounds), or trying to crush someone's face aren't considered deadly force.
* Reasonableness (would any other reasonable person in that situation fear for their life) -- If you were a naive teenager (or even an adult) and an adult said they'd kill you and then waited until you were alone to chase you into a corner, would you be afraid? Would you wonder if you were about to die?
* Avoidance -- this is the different one. Some states have clear stand your ground law. You never have to retreat from a fight if you are defending yourself. Some states have castle doctrine which says you have to retreat on the street, but not in your home or it's curtilage (the frequently used area around the house). Some states say you must retreat first in all situation up until you are completely cornered. 38 states are stand your ground. A few more like California, Illinois, or Oregon have castle doctrine. only a handful in the Northeast have duty to retreat everywhere.
Now, even if there were a duty to retreat, Rittenhouse did this too. He ran away until he was cornered and only then (and with Rosenbaum mid-charge) did he shoot the gun. Likewise, he did not shoot his gun at the others until he'd been hit in the head with a rock and collapsed to the ground a few steps later in the middle of retreating to the safety of the police line.
TL;DR -- This shooting would have been justified even in states with the most strict self-defense laws.