Green’s Dictionary of Slang

(US black) crazy.

1994		Black Sheep ‘B.B.S.’ 🎵 Straight up and down, you’ll say that ‘them’s the niggas, seven-thirty’.
1998		Big L ‘Ebonics’ 🎵 If you 730, that mean you crazy.
2000		Other Side of the Wall: Prisoner’s Dict. July 🌐 5150: A person needing mental health treatment, based upon the California Welfare and Institutions Code section for civil commitment. Other states will use different numbers, such as ‘730’ in New York.