“Williams intervened when a shoeless man tried to steal shoes from another man, authorities said. The suspect, 39-year-old Jermaine Jeremiah Brim, of San Francisco, allegedly took Williams’ knife during a struggle and stabbed him to death with his own weapon. Brim was booked Tuesday on suspicion of first-degree murder and carjacking.”
https://www.sfchronicle.com/bayarea/article/BART-stabbing-Victim-identified-in-rail-14850428.php
Terrible idea to intervene in a fight between 2 unarmed men with a knife. There was no good outcome if the bad guy was willing to fight. Either this guy was going to jail for stabbing Brim, or he was going to be stabbed himself.