BART service stopped between the Glen Park and Daly City station in San Francisco due to "a person on the tracks." According to SFGate, "BART spokesman Jim Allison said a community service officer saw a man on the tracks at Glen Park running toward the Balboa Station. BART shut down power to the rails, and agency police formed teams to search the tracks in both directions." That is to say, there is no BART service between Glen Park and Daly City. Trains are being turned around at each station.
Update: BART says riders should anticipate "a 10-minute delay at Glen Park in the SFO, Millbrae and Daly City directions due to person(s) on the track."
Update II: Service has been restored between both stations. Expect delays throughout the morning commute.