My Horse Roots At The Bit
Ninety percent of the time "head tossing" and "rooting at the bit"are caused by the person riding the horse. If your horse "roots at the bit," that is, he drops his head and pulls or tugs the reins out of your hands, then he's learned that when he pulls you give. That is, he knows that when he yanks the bit, he'll get a release from bit pressure because your hands will move in kind. The head-tossing horse has learned the same thing.
It doesn't take a horse long to realize that he can move your hand. The opposite would be true if you were to tie him to a tree. He'd pull a couple of times and realize there's no give. He'd quit pulling; there's no point. If your horse yanks at the bit, then pick it back up and be ready the next time. You want to try to catch him before he can yank that bit away by being prepared to hold it steady. When you take ahold of the reins, lock both your fists behind the saddle. That'll give you the leverage you need to hold on the next time he gives it a good yank. Hold until the horse softens and then give the reins back. Until your horse gives you back his head just the way you want him to, you just keep picking them up, asking him to soften again - and again and again.
The same thing will happen if you release too quickly. If you were to give the reins back very quickly (and very often), some horses will begin taking their head back very quickly (the head tossing/slingshot/snapped rubber band effect). If that happens, simply make the horse keep its head in position, waiting a little longer before releasing. Just keeping putting his head back, practice your timing - and release on "politeness" from your horse. Say to your horse "If you're going to take your head back, take it back with manners." If that little voice in your head says your horse is playing you - he just might be.