Former Brooklyn high-school basketball star Lance Stephenson shoved his baby mama down a flight of stairs and slammed her head into a concrete step after she refused to take his phone calls during a girls’ night out, cops and pals said yesterday.

Jasmine Williams, 21, had been the victim of the temper of Stephenson, 19, before, a family friend said, but she allegedly kept quiet because she didn’t want to hurt his hoops career.

She took out a restraining order against him after the incident early Sunday at her Gravesend home that left her with head and neck injuries.

His lawyer, Al Ebanks, denied the charges.