Kansas City Police Chief Graves said they were investigating whether the gunman was protected by Missouri’s “stand your ground” law, which allows people to use deadly force if they believe it will protect them from death or “great bodily harm.”
But as investigators and Lester’s legal defense look to the self-defense laws that may apply in this case, Sean D. O’Brien, a professor at University of Missouri Kansas City School of Law, tells TIME, “There’s still a reasonableness standard. He has to be able to point to something to say he was in fear of [the] ringing [of] the doorbell, and [Yarl] being Black by itself is not going to cut it.”
https://time.com/6272343/kansas-city-ralph-yarl-shot-protests/
Seeing an unknown young black man who forcibly enters your home without invitation after ringing the doorbell is a dammed good reason to be in fear of losing life or experiencing great bodily harm.
In fact, the man does not need to be black or young. Race is the most minor factor in a probable response. The pattern is "home invasion". The assessment and response choices must be made in about one fifth second if the door is already open.
The most probable correct response is to shoot the intruder immediately. That is particularly so if you are older and not able to physically resist the person in front of you. There are no second chances if you guess wrong.
Notice how the story keeps changing with additional details being disclosed.
Was the door opened before shots were fired or afterwards?
Who opened the door?
Did the young man enter the home?
Did the young man say anything to the homeowner?
Did the young man touch the homeowner?
I expect the young man was convinced that his siblings were in that house and was righteously aggressive, belligerent, and demanding that the homeowner produce them. Not smart tactics when approaching an unfamiliar residence.