The planet Spandle within the NoCoZo is well known for its unique birth-control system. Spandle allows complete free-breeding, but also has the Murder Lottery. Due to its complete free-breeding standards, it is a sought-after living location within the fairly heavily regulated NoCoZo. The catch is this: Every one to two local years (approx 325-650 standard days or 334-668 local days), the Murder Lottery takes place for a period of 10 local days. Anyone who has retained free-breeding status at any time during the last 4 years and are beyond the age of puberty are entered into a vast lottery on a previously unannounced day. The winners of this lottery are those who are capable of killing at least 3 of the names drawn during this 10 day period. The number of names drawn at any one time is one percent of a number proportionate to the population overpressure, plus 1/3rd.
During this period, weapons regulations are severely relaxed, to the point where any me lee weaponry and any non-explosive subsonic round may be used. Chemical weapons are allowed, but only in contact or injection vectors and must be one of 5 different 'stun' or 'psychotropic' formulae, which are determined at the beginning of any of the lottery days. Note that termination of someone whose name has not been drawn is an automatic death sentence.
Thus, families often gather together to protect their breeders when the Murder Lottery comes around. The problem is, people come and wait in subsistence conditions in orbitals for a chance at the Murder Lottery. And they have access to public-area surveillance records and public information on those who've been in active-breeding status in the last 4 years, including last known living location and hi-res holographic motion footage.