Beat Up events are first unlocked after the memory ‘Beat a Cheat’ in DNA Sequence 1 but none are available until DNA Sequence 2. You can locate them on your map by pinpointing a icon. There are five Beat Up events available to you throughout the game. Completing just one will unlock this achievement.
The first available Beat Up event in Florence is called ‘A Woman Scorned’. It is available after you complete the first DNA Sequence. When the next sequence starts, you will automatically be speaking with Annetta, your family’s live in servant. After that conversation, turn left and you will see a woman glowing white. Press to speak with her to find out that her husband is being unfaithful to her and wants you to beat him up. Accept the mission and when you have control again, follow the yellow crosshairs until it disappears and becomes a green circle on your mini-map. Activate your Eagle Vision (hold ) to locate the husband who will be glowing yellow. Simply beat him up as you did your sister’s boyfriend and the achievement will unlock.