The man, who the police said was homeless and whose name was not released, was pushed onto the northbound tracks at the 72nd Street station by a woman who then fled on foot, witnesses told the police. Soon after, the police arrested Carolyn Mack, 23, of the Bronx, on an assault charge. (She told investigators she did not push the man.) He was knocked unconscious after hitting the tracks, but regained consciousness before he was taken to the hospital, the police said.

Mr. Davis, a native of Greenwood, S.C., who has been a member of the corps de ballet at Ballet Theater since 2007, was not dancing on Saturday because he was recovering from a herniated disk. But his wife, Cassandra Trenary, a soloist, had danced in both the matinee and the evening performances of “The Golden Cockerel” on Saturday, and they were leaving the theater, with his mother, when the incident unfurled.

They normally use the 66th Street station to go home from Lincoln Center, but there were service disruptions over the weekend that sent them to 72nd Street. As they waited on the downtown platform, Mr. Davis said, they watched in alarm as an altercation between a man and a woman on the uptown platform turned physical. The police said the two did not know each other but had been heard arguing. Ms. Trenary sent Mr. Davis to look for help.

When he went upstairs, he said, he found no one in the token booth, and he went down to the uptown platform just after the man had hit the tracks. Then, he said, he decided to jump down. It was only later that the danger sank in.

“It was really scary,” he said. “I don’t know if I had time to process it until I saw my wife coming down crying — then I realized it was scary.”