Once the mission starts drive to the marker to meet Cesar. It will be helpful to have full health and armor for the latter part of this mission so if you don't have them already this will be your last chance to grab them. Once at the marker watch the short cut scene then drive to Sweet's marker. Once there just keep shooting Balla's until the cops show. You will be transported by Tenpenny and Pulaski to a new area of the map. Once this happens the trophy will unlock.