The naked acrobat filmed last month accosting passengers in a San Francisco BART station pleaded not guilty to charges of false imprisonment and battery Tuesday while his worried friends looked on and said he needed psychiatric attention.

Yeiner Perez Garizabalo, 24, who goes by the shortened Yeiner Perez, barely spoke at his first appearance in San Francisco Superior Court except to answer "yes" to a few questions posed through a Spanish-language interpreter.

Perez pleaded not guilty to two felony counts of false imprisonment, four misdemeanor counts of battery on public transportation property, and one misdemeanor count of sexual battery. All stemmed from a May 10 incident where he was filmed running naked through the 16th Street Mission Station and touching several passengers, allegedly injuring at least one.

He had been performing for months with Berkeley circus troupe ClownSnotBombs and showed increasingly erratic behavior in the weeks leading up to the incident, fellow circus members said.

He'd become prone to outbursts, said Ben Goldstein, a musician with the group. In the week before the BART incident, he struck one of the troupe, said clown Faeble Kievman.

Then on the afternoon of May 10, as the group rehearsed for a show that night at Stage Werx Theatre on Valencia Street, Perez's demeanor suddenly changed.

"We said, 'Hey, are you all right?' " Goldstein said. "He had this blank look. He just walked out of the theater."

Prosecutors say Perez walked a block to the BART station and began grabbing riders. He was arrested there and held overnight at a hospital, then in jail for two days.