horse headbutts and rears

Question
hello sir, i have a 4 year old thoroughbred race gelding. he always head butts and rears while leading to the track. trainer appointed a boy to sit astride that horse. still no use. horse didn't change its habit of rearing. he's a good runner. in the morning workouts, he is only trotted. if he's broken to canter by any rider, he would take a U turn as if disagreeing and messes up in the track. may i know what is the problem with the horse? how to fix its problem?

Answer
This horse is showing massive disrespect for humans. The only way to fix the problem is to start over again from the beginning. It needs a solid foundation from the start. There are too many missing training issues to correct. If the horse is started over from the very beginning (as if it were never trained) and these issues were delt with, the problem would not exist.