It's no secret that in Los Santos (as in all San Andreas) raging crime.
And as in any big city in America, there are some areas and alleys, which are "under the authority" of local gangs.
This lane there and in Los Santos. It is close to the "Ammunacii" (shown in photo). Come back gently. If there's someone you can attack!
After entering the lane will start something like "mission" you will need to kill all the attackers and then try to catch and kill the gang leader. If you succeed, you collect his money.