“I saw him hit the old man,” said witness Ali Thomas, 24. “One hit. He swung hard. He hit him hard. The old man’s head hit the curb.”

The 911 caller said initially that the 56-year-old was in cardiac arrest after the fight, according to fire officials. He was taken to Bellevue Hospital in stable condition, officials noted.

Cops arrested the alleged assailant, David Campbell of Crown Heights, Brooklyn, authorities said.

Campbell, 30, was charged with assault for strangulation, possession of a weapon, assault of a police officer, resisting arrest and loitering, police said Sunday morning.

Two more people were hurt in the brawl. One person was taken to Mount Sinai St. Luke’s, while another went to Bellevue. Their conditions and involvement in the gala were not known.

Cernovich later emerged from the event and confronted a group of demonstrators. “These guys are f—–g terrorists,” Cernovich said.

The Night for Freedom event — billed as a “gathering of patriots and political dissidents who are bored with mainstream political events” — featured a comedy routine, speeches and a deejay set.

Perhaps the most surprising guest at the event was Chelsea Manning, the transgender former Army private convicted of the largest leak of classified documents in American history.

It was not clear why Manning, who was planning to run for a Maryland Senate seat as a Democrat, attended the conservative gala.