This article is a Stub.
There's fairly well-documented cases and study of the effect that witnessing people being abused or traumatized is in itself traumatic.
Some abuse involves being made to witness abuse, in which case it could be called "witness abuse". Other times the witnessing itself is not intended, although the situation may be intentionally abusive towards someone else.
Witness trauma is acknowledged as a specific type of trauma in Melody Beattie's works Facing Codependence and adds a layer of "survivor" guilt to the situation for the witness not being able to defend the victim, in addition to the fear/avoidance issues of not wanting to be hurt or victimized oneself.
People may see siblings being abused, or parents abusing each other, may witness a car accident or other traumatic situation, or in the case of folk who are multiples, we may have witness abuse from being coconscious and unable to help one another due to being locked out of front, or being in flight mode and avoiding being the victim while paradoxically wishing we could save the headmate receiving the trauma.