First things first. How many times has he done this? Does he always act poorly around the gate? Or does he just act "stupid" randomly? If it's a gate issue, I would suggest groundwork around the gate - put him on a lunge line and work him at all the gaits, and make him work through his misbehavior. A lot of horses (mine included) like to "duck out" at the gate, but a little groundwork goes a long way!
When you work him, be confident and assertive, and try not to let him see you get frustrated - horses pick up on that and remember, he's NOT a person - your frustration/disappointment won't make him try harder - it will make him act up more, because as you lose control over your emotions he will take advantage. If you can't ride or work him without losing it, then have someone else work him. Maybe take a break for a few days. If he does act up, make sure to work him through it - if you put him away after he misbehaves without immediate correction, then all he has learned is that misbehavior puts him back in his comfy pasture. Make sure the bit you use isn't extremely harsh - anything in his mouth will be a step up from a hackamore, and a harsh bit isn't the solution to a training problem.
How long have you and this horse been working with the drill team? Maybe you are asking too much, too fast - does this horse reliably walk, jog, lope, stop, and back on command? By himself, and also in a group? If he doesn't, then that's where you need to work before you even think about showing. If showing in drill team is really important to you (and it sounds like it is), maybe see if you can ride a different horse. Don't rush Blu - if you push it too far this season to get him to a show, then he might never make it to shows in the future. Showing is fun, but not at the expense of good, basic, training.