Humans are entitled to use deadly force in response to credible threats to life. Someone waving a knife around, or even running while waving a knife around, is not that. The fact that knives exist is the reason that police carry billy clubs. A normal who citizen shot and killed someone of his own race because they were waving around a knife, would be charged with murder. Police officers should be better trained and better able to deal with knives than the average person. Those few departments who have mandated effective training have seen significant results from that training. [0] Well-trained ninjas with swords are actually quite rare in the modern policing environment.

[0] https://www.jiujitsutimes.com/marietta-police-department-imp...