90% of self defense cases end in the tribunal, meaning that the judges saw it as not-self-defense. The biggest factor in all this is proportionality: if you killed someone in self defense but were not yourself having your life threatened, you will go to court.
Any physical assault is potentially life threatening. One unlucky fall on the pavement and that's it - you can easily die or become permanently disabled. Yet another reason why it's better to deescalate and/or run away if possible.