To unlock the Frenetic Player trophy in Cities: Skylines, you will simply need to inspect a police building 50 times in a row.
You unlock the ability to purchase a Police Station once you hit the Worthy Village milestone for having a population of 240 - 950 depending on which map you start on.
Once you have built a police station, use the inspector tool (house and magnifying glass symbol) and click on the police station you have just built. This will open up the police station's info window. Back out to close the window. Repeat 50 times until the trophy unlocks.