What a terrible end for that poor horse. But I too don't really blame the original poster about it. I mean, sure, there's common sense....but when you're listening to a supposed professional.....
Before I even knew there was NH and all that common sense horse stuff, I went to a couple of what I call "whip and spur" schools of training where the horse was treated like a tool. I recall a mare that took 3 of us to saddle....and when the hobbles came off and the trainer who was supposed to be teaching me...let go of the lead line that was wrapped around the post...the horse reared straight up and kept flipping over and throwing herself over. Luckily she didn't injure herself. But I look back on all of the crap that went on at that place and think...geez....how stupid could I of been to of trusted these morons? But I did. Luckily, I saught out better ways and found em.
The disgusting part is that there are a lot of so-called trainers who are more than willing to rush the horse through so-called training to get them the hell into the arena to win win win some money. If the horse breaks down, who cares, get another.
One of the horses that I've posted a lot about around here somewhere....who was started badly by a cutting horse trainer.....a well respected ass-clown who unfortunately wins enough money each year to be able to torture a new batch of prospects. Now, I'm restarting the horse that he threw away.
Anyhow...enough of that...
How to get vertical flex from a green horse?
answer: lateral flex
If you have no lateral flexing, you aren't going to get vertical flex. The horse has to understand giving to pressure by way of the reins/bit first, and that comes easily through simple lateral flex exercises like:
-one rein stop
lateral flex means the horse's neck bends easily when slack is taken out of the rein and the horse "gives" to the pressure by bringing his head around BUT that's just part of it....you want to add the hip, too. That is,...you get the neck to bend and flex AND you ask that same side hip to move over (so left rein = left side flex and left hip steps to the right) and this crosses the hind feet and this also puts a bend in the body, which...think yoga for horses....it causes the horse's mind to relax and the whole body starts to relax and "give" to pressure.
The more lateral work you do, the better and easier the vertical flex work will happen. It'll be the gradual next step.
an easy next step to lat. work to get vert. work:
3 step stop
1) go forward
2) pick up both reins as you roll your hips forward (squeeze the butt cheeks)
3) take out the slack but never pull back, just lock your hands on the saddle swells or your legs, low hands are good! high hands are bad. hold that and wait.
4) when the horse stops and flexes vertically let the reins go (release)
5) repeat. repeat. repeat. til the horse breaks at the poll easily with light pressure.
The point is an unbroke/green horse gets scared from pressure coming from both reins. It's very scary to a horse that doesn't understand pressure. So, you never want to ride a horse like that with 2 reins right from the start. You ride with one rein at a time to let him get used to feeling pressure on the right side and then on the left side....when he's giving willingly and calmly to either rein pressure...THEN you add both reins.
But you also want to go back to one rein vert flex at higher speeds. So, at a trot, I'd pick up one rein and ask for a give. release when I got it. Then pick up the other rein and do the same. Then I'd use both reins eventually when the horse is responding well to either rein. same at the lope.
It's about preventing issues and preparing the horse for the next step.