A train operator reported that as he was passing through the fare gates, a male followed him into the paid area without processing a ticket. The train operator tried to stop the male, who brushed by him and chest bumped him on his way to use the restroom. After using the restroom, the male exited the station and went to the bus zone. A responding officer located him and detained him until the train operator responded and identified him as the person who bumped into him. The train operator, who was not injured, wished to place the male under citizen's arrest for battery. The male was issued a prohibition order and a citation for battery on a transit worker.