Originally Posted by Tyger7
Eye Witness 10
Witness a predator killing an enemy.
Predators are Bears, Bobcats, Cougars, Wolves, Foxes. There are a bunch of scripted events in the Frontier area where one of these animals kills a hunter. They have fixed locations and can happen at any daytime. Go to the Packanack hunting zone on the western part of the map. There is a road going from north to south. Follow the road until you come to a restricted area (highlighted in red). Go up a hill to the west and you will encounter several bobcats, as well as two hunters. You may not be in open conflict with any of the hunters or animals! Otherwise, they won't attack each other. Don't shoot or harm the bobcats, they might run away. If you cannot get this done on the first try then get yourself killed and everyone will respawn. Just wait until one of the hunters runs into a bobcat and keep watching.
Assassin's Creed 3 - Eye Witness Trophy / Achievement Guide - YouTube
I can confirm that elk also count for this achievement. I just saw a redcoat get rammed by one when I was on my way to a Hunting Society mission in Valley Forge. Achievement unlocked.