Yeah - it is not a fun experience. I think I wrote about this in another post about Mustangs and dominance.
My second or third paying job breaking horses was with wild caught Mustangs. Now, these girls were not fresh from the wild, but instead had spent a couple years at a fancy training stable... When I got them in to train, both had been saddled, and 'bronc' ridden. One had been ridden out twice, one had tossed all takers. These two girls were both about five when they came to me. I was 15.
The one who had been 'ridden down' would attack you if you turned your back to her. She would rear and strike, but mostly just sink her teeth into your shoulder. She was the easy one to work with.
The other girl prefered to do her attacking when you were facing her. Thank goodness she was only 14.1 hands. She would periodocially rear up and strike at my head and face. About the third time I came home with bruises on my chest from these strikes, I sought help of another trainer. With a more experience trainer present, we set about our normal workout.
I caught the mare using carrots, groomed her, and then started lunging. I was lunging for several minutes when the horse turned on me. She reared up and showered my head and shoulders with strikes of her front hooves. This time, she knocked me to the ground. Once I was on the ground, she proceeded to do her best to crush my rib cage flat by rearing and coming down on me as well as pawing and biting at my face.
The only reason I lived through the experience was that the other trainer was right there. The moment I was attacked, she attacked the horse with a lunge whip. It took her about six or seven minutes of whipping the horse to convince her to break off the attack. I got through it with several broken ribs and more bruises that could be easily counted.
The odd thing is, eventually that little mare was given to me. With enough kindness she eventually because a lap pet and a great horse. Once she figured out that I was not going to hurt her, she became kid safe. She was fantastic to work cows with, and could jump to four feet. By the time she was ten, she would have made a great kid's horse, but stayed my extra riding horse and was used on occasion for my sister's kids until we lost her to cancer in her late teens.