Unmanageable at competitions?

Take him to a few shows without entering him in any cles and work with him to calm him down. Saddle him up and walk him around through the other horses so he has to get used to it. I did this with a mare that I had and she eventually ame around. I'm going to do this with a friend's horse as she strikes out at the person leading her with her front legs quite a bit whenever she gets overexcited.