"What is Danny supposed to do?" Kitty, whose real name is Kathryn Beckwith, said on the Noisey video website.
The experimental 32-year-old hip-hop artist -- whose 2011 album "XXX" was named Spin music magazine's No. 1 hip-hop album of the year -- was in the middle of a song when the unidentified fan came up and pulled his pants down.
He had invited some female fans to get closer to him, the AllHipHop news website reported.
"I'm mad that a person thought it was OK to pull another person's pants down during their performance in front of about 700 other people," Kitty wrote.
"I'm mad that a person thought it was a good idea to perform a sex act on another person without their consent. I'm mad that nobody made her leave. I'm mad that Danny had to actually wonder what he was supposed to do at that point," she wrote.
Pushing the young woman off would have brought on "attacks on his masculinity" from other rappers, she said.
Even the "most gentle" action to move the woman away "would immediately be labeled 'abuse' by anyone watching," Kitty said. "Guys pushing girls is not a good look when people are taking photos. So what was Danny supposed to do, other than back away, which he did?"
Brown, whose real name is Daniel Dewan Sewell, initially responded to the Friday incident on Twitter, saying that despite the distraction he "didn't miss one bar" in his performance.
He later deleted the message.