The Mission has a big gang problem. There are a few very violent gangs that hail from Mexico and South America there. I also think Bayview has a violence problem. There are often reports of police seizing guns from people in that area. Western Addition is also a problem. Around Eddy and Laguna, you'll hear of the "Eddy Street Gang." They hang around the housing projects in this area.
Lastly, I'm not sure if this is a result of "gang violence," but the area around 6th and Market has a lot of crime. It could be due to the large amount of homeless men that loiter there.
