Aggressive Behaviour
Horses are not born aggressive! They can become aggressive because...
The Grass
They are consuming ‘bad’ grass with clover, especially red clover, which affects their hormones. For example, this can cause geldings to exhibit stallion-like behaviour. People mistakenly think that the horse hasn’t been gelded properly, the vet is called, bloods are drawn but results prove otherwise.
Miscommunication
You are ‘p.....g them off’!!
The communication between you and you horse is not good enough, he isn’t sure what you mean and you are making him feel wrong when you weren’t clear in the first place.