The best method is to deal with all the gang members before attempting to take out the Gang Leader. Once all the gang members have been taken care of, get ahead of the Gang Leader and hide behind a corner along his path. Once he's in range attack like normal or throw your weapon at him, knocking him down and finishing him off with an execution.
- The gang leader is found at the end of the level in the last section, and can be identified by his unique appearance and weapon. Upon entering this zone the leader will talk briefly.
- If the gang leader spots the player, the unique clank of the leaders metal pipe can be heard. This will alert all gang members in the area to the players presence and means they have failed the requirement for this achievement. However, the player can just allow themselves to be killed, restarting this zone and allowing the player to get this achievement again.
- This achievement is much easier when in rage mode