In order to get this trophy you need to complete a 'Race Event' which is denoted by the Checkered Flag icon on the map, go to the thief and press
to speak to them, they will give you a course in the city to run with a do able time limit. Run through the markers on the map in order to the finish line to get this trophy. There will be free-running and jumping over rooftops involved but you should have no problem beating the time.
Note: Races are unlocked after the 'Paperboy' mission