Chapter: Lexington Station
During this chapter Ethan will have a fit of sorts and everything will freeze, to get this trophy you have to knock down 50 people inside the station, this is simple as long as you know where to walk.
During the cutscene you will notice a large statue near the front of the station, this is where most people are standing. Make your way to this statue and around it and you should have no problem unlocking this trophy.
Reminder: Trophies don't pop until the loading screen appears for the next chapter.