This trophy comes from Chapter 10 - Historical Research.
Follow Elena through the first part of the chapter, and you'll start a chase with Talbot. You'll grab your notebook from him as he throws you into a market place and immediately you'll be set on by a few thugs. This is the area you want.
In the middle of the little square are two tables arranged in an L-shape, with three or four fish on it.
Dance around the baddies and get yourself over to the table, when one of the thugs approaches, push your analogue stick towards the FISH and push
. If you've time it right you'll smack the guy down.
You'll need to move around the table as you go, there's two on the opposite side, you'll need to move around into the seat of the L-shape. After the third smack, the trophy should pop.