Patrons on board the Millbrae bound train reported that a male suspect was acting erratically and brandishing a knife, while making verbal threats. The suspect fled on foot, dropping the knife, when officers arrived. Officers captured the suspect on the street above the station. None of the witnesses wished to pursue a criminal complaint against the suspect. Officers determined the suspect was in need of emergency psychiatric detention. The suspect was transported to SF General Hospital for evaluation and treatment. The train was delayed about 5 minutes as a result of this incident. There were no injuries. TSOC notified.