I would have his teeth checked. I knew someone who owned a mare who appeared crazy. She was nervous, spooky, reared and bucked. They tried a flash nose band to keep the bit in place and then she really went berserk! Nobody wanted to train her because she was so wild. I suggested that they have her teeth looked at and they found they were cutting into the inside of her mouth. Once her teeth were done she turned into a perfectly sweet and gentle horse.