Amazing photos... I also have to assume that buck was already hurt or ill, something was wrong with it and those yotes took advantage. Still wasn't easy for the yotes, took hours to get the buck down.
That buck is clearly dead. It doesn't move for hours and the yotes ate the back half of him out and the buzzards were picking at him the next morning. Also, the guy was holding the skull of the deer at the end!
EDIT: Here is an individual pic, I am pretty sure that's a dead deer. http://www.deeranddeerhunting.com/wp-content/gallery/coyotes-kill-buck/455.jpg