Police say that the girlfriend was treated at the hospital for head and neck injuries.
Stephenson, who starred at the same Coney Island high school that produced Stephon Marbury and Sebastian Telfair, was booked on assault charges.
The leading scorer in New York state history, Stephenson spent one year at Cincinnati and is no stranger to run-ins with the law. In 2008, he was busted for sexually assaulting a 17-year-old outside his high school.
It's unclear what prompted the violence.