He would have to provide compelling evidence to the court that the mother is unfit and it would be in the child's best interest for him to be granted sole custody.The factors used to determine that a parent is unfit are generally governed by state laws with child endangerment being the determining factor. The following include some of the reasons a parent may be declared unfit:physical, emotional and sexual abuseexcessive disciplinefailure to protect the child from abuse by othersfailure to report abuse of the childneglect- failure to provide food, clothing, proper hygiene, necessary medical treatment, schoolingfailure to provide proper medical carefailure to provide day to day parental careserious illness or disabilitymental illnesssubstance abuse or addictionAlcoholismcriminal activity and/or associationsincarcerationconduct or conditions that are seriously detrimental to the childabandonmentchild endangermentleaving the child unattended or in the care and supervision of a child or otherwise incompetent persona failure to provide adequate supervisionunsafe living conditionsa medical condition that makes it impossible for the parent to adequately care for the childleaving the child in someone else's residential-type care for extended periods of time