An officer contacted a male subject who was smoking in a prohibited area in front of the fare gates at the Concord BART station. The subject became uncooperative and started to walk away from the officer as he was trying to detain him. The subject slapped the officer's hand when he tried to grab him in order to prevent him from walking away and then began to run away from the officer. The officer eventually caught up to the subject and held him at gunpoint in an alleyway between residences in the City of Concord. It was later determined the subject had discarded a firearm prior to surrendering to the officer. The subject was taken into custody with the assistance of officers from the Concord Police Department and was found to be in possession of a small amount of methamphetamine. The subject was booked into the Martinez Detention Facility for all of his violations.