Self defence is not antisymmetric, as a contrived example suppose two people are independently running away from murderers and bump into each other in the dark

Self defence is not antisymmetric, as a contrived example suppose two people are independently running away from murderers and bump into each other in the dark (maybe add some extra factor like a gunfire sound starting at the same time) then both would be covered under self defence to use (deadly) force againt what was actually an innocent victim.