According to police, Brock was arrested a short time after officers responded to a report of a domestic violence incident. Upon arrival, officers found a woman who had visible injuries and learned she was dating Brock.
Police arrested Brock, 28, and he was booked into Santa Clara County Jail. He was released Friday afternoon, according to jail records. He was later released by the 49ers, the team announced.
The veteran cornerback started in every game for the 49ers over the past two seasons. Last season, he recorded 59 tackles and an interception. Brock has played his entire seven-year NFL career in San Francisco after joining the team as an undrafted free agent in 2010.