Jonathan Josey, a former lieutenant, was at an arbitration hearing on Monday.
Josey was videotaped punching Aida Guzman after the Puerto Rican Day parade last September. She was struck in the face and fell to the ground.
During his trial, Josey testified that he was trying to knock a beer bottle out of Guzman's grasp.
At the time, the judge said the video was 'disturbing,' but said there was insufficient evidence to convict Josey of simple assault.
Guzman settled a lawsuit against the city for $75,000. She was at the hearing on Monday and emerged shaken and crying.
"During the arbitration process she was attacked, her credibility was attacked, they were calling her a liar and basically taking the situation and trying to twist it around on her, trying to make it seem - once again - that she did something wrong," said Guzman's lawyer, Enrique Latoison.
Latoison also said he expects Josey to be reinstated.
"The FOP has negotiated a project that is very powerful for them, it allows them to take officers who commit this kind of behavior to be reinstated," he said.
Police Commissioner Charles Ramsey, who also testified at the hearing Monday, is fighting to have the firing upheld.
"It certainly hurt the public's trust. He's got a career that cuts both ways, he's certainly done some good things, too. But I felt that particular case was particularly bad. It didn't have to happen," Ramsey said.
He added that he will be compelled to put Josey back on the force if the arbitrator rules in Josey's favor.
The hearing will enter a second day on Tuesday, with a ruling expected within a month.
