When calling Cougars, I've had one come in from behind me, and to the left, within ten yards of me. He took of so fast and furious that I wasn't able to get a shot at him. As .308 Norma sez, flinging sticks and rocks as he went! Last one came in from my left side, and he's dead. When I used to call coyotes, they often came in from behind and walked past me.
Called in two wolves when calling cougar, but they came straight in. When they saw me (20 yards) one took off, but the other slowly circled around behind me. As I had a good "back stop", I lost sight of him/her/it, and don't know where it went.
Actually being attacked by a 'yote is unusual, but if the animal is extremely hungry, and perhaps had never or seldom seen a human, I can see where the instincts could kind of just take over, and the coyote might think the human was food. ? Or once "committed", couldn't stop. I always have something behind me, rock or tree, and lay a pistol on my right, as it's very hard to swing the rifle hard-right (if right handed) when sitting on the ground.
My K-bar is also always strapped to my right leg, below the knee. !!!