This trophy can easily be unlocked during Chapter 11: Alone, and difficulty does not matter. At the beginning of the chapter, you will go into a mall and up an escalator. Follow the path around, and you will be shown Lugo and Adams surrounded by soldiers on the other side.
Simply vault over the cover in front of you, knocking the soldier over the side. This can almost be considered story-related, however you can kill the solider without kicking him. If you somehow miss this, reload the checkpoint and try again, and if you forget and move passed this point, select this chapter in the chapter select.
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