The suspect approached the operator of a train that was stopped at the station around 11:21 p.m. Saturday and spit at them, according to BART police Lt. Michael Hayes.
The suspect - only described by police as a man - was detained on an emergency psychiatric detention, issued a citation and transported to San Francisco General Hospital, Hayes said. The operator wasn't injured.
The incident sparked a major delay on the Warm Springs line in the Millbrae direction.
No further information is immediately available.