Aldon Smith was arrested again and is behind bars after cops in San Francisco say the ex-NFL star violated a condition of his bail ... TMZ Sports has learned.
Smith was booked into the San Francisco County Jail around 5 PM Friday night. He is still in custody. Jail records indicate his bond is $500K.
FYI -- the former Raiders star was in court on Thursday after allegedly violating a protective order put in place following his arrest for domestic violence. The judge ordered Smith to wear a GPS and SCRAM device -- which measures alcohol in your sweat.