We recently purchased a "kid-friendly" mule. A young child was riding him and another person was walking under him, between his legs and pulling his tail in an attempt to agitate him. The mule never retaliated. Since having an accident on a horse as a teenager and not riding since (I am now 50) I felt possibly this was the animal to help me get over my fear of riding. Two days after bringing him home my husband was in the pasture with him, turned his back and the mule reared up and came down on his back with hooves! Any idea what would cause such behavior? We are now both afraid to get into the pasture with him.
Mules can be very territorial creatures. They are highly protective of their pastures and the area that they consider to be their territory. If they feel threatened they will protect their territory with flying hooves and sharp teeth. Here in Missouri a lot of the cattle and sheep farmers turn mules out with their herds to protect them from coyotes, mountain lions and such. I would recommend bringing him into a small enclosure to feed him and catch him when he's done eating, this will prevent him from feeling like he needs to be protective. He sounds like a very well broke mule and his behavior in the pasture has nothing to do with how well trained he is. His pasture behavior is instinct.
Thank You and Happy Trails!