This trophy is story-related and cannot be missed via normal campaign progression.
For this sequence you must follow a guard to a location where you can kill him. He takes the most ridiculous route possible. It's not hard, but it's soooo long. When he gets to the location you must kill him and take his clothes for your disguise. Then you get to carry a special box to meet the Spaniard.
When you meet up with Rodrigo, you have to fight him. You can't kill him but you must wound him enough to retreat. Just keep counter attacking and he will run.
The trophy will unlock once between a few cutscenes after you have won the fight against Rodrigo.