Hancock is as well known in the field of linguistics, particularly in the area of pidgin and creole languages, as he is in the world of Romani studies and Romani social activism. In addition to his research on the Krio language of Sierra Leone, he has studied the Gullah language, of coastal South Carolina and Georgia, and the Afro-Seminole Creole language, spoken by a community of Black Seminole descendants in Brackettville, Texas. Hancock was the first scholar to report Afro-Seminole Creole. He later identified another variety of that language spoken among Black Seminole descendants in the village of in the Mexican state of Coahuila, where their ancestors had settled in 1850. He maintains that Afro-Seminole Creole and Gullah are closely related languages, as Black Seminoles were descended primarily from Gullah people of the Low Country of South Carolina and Georgia.