Hmm, how to overcome being spooky.

I agree with kevinshorses, and if you let him take off to a gallop when he wants, no matter how much fun it may be, you're always going to have a problem. If you want him to canter, and he wants to gallop, you need to keep him at the canter, or slow him down, not let him speed up.

A few things I am certain. 1) it's great you can ride him in a halter, 2) you need to make sure you are respecting his thresholds at all times...if not, that can lead to spooking, 3) work on circles so that if he gets impulsive, you can easily put him on a circle until he calms down (the more impulsive he is, the smaller the circle), 4) the worst thing you could do is punish him...spooking is a fear based reaction and to the horse, SOMETHING is worth being scared of. It might not make sense to us, but we need to put ourselves in THEIR shoes, that's part of good horsemanship. Horses do not fake fear.

I have to disagree with the opinion that all spooking is fear based. With my TB, there's a subtle but noticeable difference between when he's genuinely scared and when he's just being a goof. If it's the former, I do have to back off and do what's necessary to calm him down. If he's just being a goof, I act like nothing happened and we continue with our ride, end of story.

I had a similar problem with him this past summer. Any time we were out in the open fields and started cantering, we would quickly get into an argument about how fast we were going to go. If asked him to slow down, instant bucking fit. We went through the same routine about 7 times before he finally realized that the end result was going to be a one rein stop, and he gave up on it as quickly as it started. We were only into a slow canter when our problems started, so the one rein stop worked. I'm not sure it would be a good idea to try it at a gallop. I'd suggest just not letting him get above a moderate canter the next few trips out until he's done with his little hissy fits. You need to have some way of addressing it while still staying safe.

First you really need to ride him in a snaffle..you have no control in a halter. Also, with snaffle you can control and learn to stop him when he takes off. The fact that you let him continue running just reinforces his behavior it says you are okay with it until he starts bucking but looks like running leads to bucking so you have to stop it before it gets that far. Also, he doesn't respect that you are sitting on him when he does that like he feels he is being turned out rather than being ridden. He has to know that he can buck all he wants to get his energy out while being longed or turned out but never when someone is sitting on him. Which leads to my next note...longe him first before riding him so he gets all the bucks out before you get on him. This will also teach him that bucking on longe is okay but not with someone on him. He needs to learn his whoa, too. He really needs to be ridden in something like a snaffle. This will also teach him...when he's bridled up he must respect the rider on him.

I think I agree with kevinshorses on this one...riding a "very very green horse" outside an arena or fenced area with nothing but a halter for control while he's got teeth problems...I'm kinda surprised his blow up wasn't worse. When I discovered my 4 year old had wolf teeth, her training was PUT ON HOLD until I was able to afford her treatment a month later. I didn't try and continue in a halter and especially not out in the middle of a field...

Sometimes all it takes to prevent an accident is thinking before acting. I'm guilty of it myself every now and again, my mom's 11 year old mare lit into a bucking fit once in just a halter, no saddle, and I managed to stay on but it was a ride lemme tell you...

How many times has your horse done this to you in the field? Just the once? Every week? How often do you ride him in the field? Honestly, I'd stop riding until you're able to fix the teeth scenario.

It would be best if he was not allowed to buck any time he was being handled. I let my young horses have two days to buck under saddle while being lunged after that then no more bucking period. If a horse is allowed to buck while being lunged then pretty soon it will become a habit.

Obviously he does not stop when told or you wouldn't of had to bail off of him.

In order to circle correctly (and thus bring him down and prevent the bucking), you need to be able to pick up his shoulder. Halters do not allow for that precise of a direction.

I agree with Kevinshorses about the lunging.

Lunging is for training in my opinion and your horse should know that it MUST behave when around humans (especially on the ground). The last (well almost) thing I want a horse to think is that it's ok to buck around and act like a nut when I'm 30 ft away on the ground training him.

OP- If your horse does this regularly at a lope you shouldn't be loping him out in a field in a halter. Were you bareback too? Just asking for trouble. You're teaching him some really bad habits right now that are going to cause you even more trouble in the future. If he's good at other gaits, you should work him on loping in a controlled area with a bridle/saddle/helmet. Learn how to stick a buck too . Not trying to be mean about it, I've been thrown/fallen off before, but I'm not a fan of bailing off a bucking horse. I've seen people get hurt worse coming off than they would've if they had just stuck it out. Others had good suggestions to specifically deal with the bucking.