After meeting the final faction during the campaign you’ll have access to the first of the Take Back the Streets missions. There are four in total and these are given to you by Floyd near the top of the middle island (located right next to the Downtown fast travel).
These missions have you replacing flags around the city and then defending them for a short amount of time. The name’s of the missions are:
-Take Back the Streets: Downtown
-Take Back the Streets: Old Factory District
-Take Back the Streets: The Harbor
-Take Back the Streets: Little Tokyo