Mission: Fight Night
Requirements: Patriot's Disguise
In the very first area of the mission, sneak left and continue around. You must get behind the RV. Once you do so, sabotage the generator and hide. A member of the Patriot's entourage will come to check it out. Subdue him and take the disguise, then hide the body. Now go around the RV and grab the radio. You should also see a teddy bear on a chair. Grab it and hide behind the containers. Eventually the Patriot will notice his good luck charm is missing and will send his men to find it. After they are far enough away, drop the radio and play it. When the Patriot comes to investigate, take him out and use his disguise. You can now exit through the door you knock on at the start of the area. Walk through and straight to the ring where Sanchez is. Follow the prompts to take him out and gain the achievement.