This horse is tied too low to the ground. What happens in this case is the horse can get his feet caught in the rope. He can fall and injure himself. If he is tangled in the rope, you must quickly and calmly release the tie. Stand back as the horse frees himself.
If the horse pulls back when tied too low, he has too much leverage and can snap the rope. Once a horse learns that he can break a rope, he will try to do it again. This can create a dangerous situation in the future, for both you and your horse.
Tie your horse level to or above his nose, and withers.