A television journalist working on a story about the controversial painting of President Jacob Zuma, tried to stop one of the men who defaced the work on Tuesday.
Iman Rappetti, eNews channel anchor, was in the Goodman Gallery in Rosebank, close to the "The Spear" when a man took out a pot of paint and marked an X in the genital area of the portrait.
She said she grabbed him, while shouting to gallery staff to come and help her. "It was surreal."
Rappetti described the vandal as a completely "ordinary" looking critic wearing a tweed jacket. Unbeknown to Rappetti another man was standing behind her with a large pot of black paint.
The second man started "going to town on the picture", she said.
"I was screaming."
Gallery staff apprehended both men and the police arrived shortly afterwards and took them away.
Rappetti said the gallery staff had told her the first man had identified himself as an Afrikaans journalist. He had visited the Goodman Gallery before.
"He did not sound Afrikaans to me," she said.
The second man appeared to be working with the first one. The gallery closed after the vandalism, and the public and reporters crowded outside.
Inside the gallery gate were three private and armed security guards wearing bulletproof vests -- with one guard carrying a rifle.