A judge released Stephenson, 19, without bail late Sunday night after his arrest on assault, menacing and harassment charges.
Prosecutors had asked for $7,500 bail.
Authorities say the confrontation occurred around 5 a.m. Sunday when the victim, Jasmine Williams, was returning home to her apartment building with two friends. Witnesses said Stephenson was waiting for her and yelled, "Are you kidding me?" before pushing her down the stairs.
A criminal complaint provided Monday by the Brooklyn district attorney's office said that as Williams lay at the bottom of the stairs, Stephenson picked up her head and slammed it on the bottom step.
When police arrived, Stephenson told them the woman had fallen down the stairs, prosecutors said. The complaint said Williams suffered head and back wounds, and possible damage to her neck.
Pacers president Larry Bird has said he was aware of the situation. Stephenson attorney Alberto Ebanks didn't return phone and e-mail messages Monday.
Stephenson was one of the nation's top high school prospects. He played one season at Cincinnati before applying for early entry to the NBA draft.