Jailhouse lawyer. (n.d.). In YourDictionary. Retrieved from https://www.yourdictionary.com/jailhouse-lawyer
(plural jailhouse lawyers)
(informal) A person incarcerated in a prison, jail, etc who has acquired significant knowledge of the justice system and who is able to represent himself in some legal proceedings and to provide legal advice to other prisoners.
English Wiktionary. Available under CC-BY-SA license.