When crime stats say "gangs" they're not just talking about a street gang with a name, list of members, defined territory and stuff like that.
They're also talking about people who engage in business that is not state sanctioned and therefore have to settle disputes with their own violence instead of getting a court to threaten state violence on their behalf. One part time drug dealer rounding up a couple buddies and putting a bullet in a guy who ripped him off will show up as and makes up a huge chunk of what's considered "gang violence" in these stats.
When comparing cities it's useful to differentiate between random crime and crime where the parties to know each other.
The scary part of SF homicides now that you can be walking around and some crazy guy just shoots you or stab you without any reason whatsoever. They are not professional criminals: they are just so drugged up or whatever.
They're also talking about people who engage in business that is not state sanctioned and therefore have to settle disputes with their own violence instead of getting a court to threaten state violence on their behalf. One part time drug dealer rounding up a couple buddies and putting a bullet in a guy who ripped him off will show up as and makes up a huge chunk of what's considered "gang violence" in these stats.
When comparing cities it's useful to differentiate between random crime and crime where the parties to know each other.