A rape gang pursuing Tasha Yar
Rape gangs were groups of men and women who would prey on lone individuals on the planet Turkana IV for the purpose of sexual assault.
From 2342 to 2352, Natasha Yar evaded the rape gangs by hiding. (TNG: "The Naked Now")
While experiencing the effects of polywater intoxication in 2364, Yar mentioned the harrowing experiences of her childhood to Data. (TNG: "The Naked Now")
When the USS Enterprise-D found itself at the edge of the known universe later that year, Yar envisioned herself back on her world. In the vision, she found a cat. Hearing the sound of the approaching rape gang, Yar said to the cat, "Now run. This place isn't safe at all." Soon afterwards, the lieutenant returned to the reality of the starship. (TNG: "Where No One Has Gone Before")
In 2367, Worf reminded Beverly Crusher of the dangers of Turkana IV's lawlessness, including these gangs, when the doctor was preparing to head to the planet's surface, but she assured him she could handle herself. (TNG: "Legacy")