Odd behaviour

Question
I am have a 7yr Tb, he was breed to race i am lead to believe had some training as a racehorse but was never professional raced he has a 2 yr period off little to  no work and i have had him 4 months. Am getting on well for the most part he is not what i would class typical Tb he is generally relaxed, gentle willing to please, quiet on hacks, is stiff and unbalanced in the school but i have introduced lunging to help this he is taking well to it. His one problem is when being riden in the school he will cope with so much then get all tense and stop refusing to move ( i had put it down to maybe being alittle overwhelemed which has been allowed to progress into avoidance) i have taken him back a step and have been doing short periods of basic work keeping it moving and constantly changing rein doing circles etc to keep him focused it had been going well. Today he did it on a hack and it was an unexpected response to the situation, the first time was when a horse cantered first in front of him he halted got all jumpy and after a push we had a standing start to gallop, once going forward he gave me back control very quickly and i was able to bring him in and out of canter when asked, we went for a second canter again the other horse went first he stopped refused to go forward he seemed full off adrenaline ( fast respiration twitchy muscles etc) but wouldnt go forward, he just froze the other girl came back and we decide it best to walk them home again he still wouldnt walk, we put the other horse behind him and he went forward but very exicted trying to canter at walk speed i refused to let him go any faster trying to get him to settle but after a few strides he again stopped and this time i couldnt get him  moving and had to dismount and lead him home. I understand the tb in him wanting to race and getting over excited but dont understand why that would related to him stopping it almost like he switches off, as i cant understand his behaviour find it difficult to decide how to help him, it also makes me wonder if his behaviour in the school is related and if i have it all wrong. Any ideas would be great

Answer
Hello Terr,
I would start with teaching him to disengage his hind end. When riding draw one rein up to your belly button and wait until his hind foot on that same side steps deeply underneath him. As soon as he begins to step give on the rein, let there be no pressure for a bit and then repeat on the same side until it feels like he easily moves from a walk to disengaging and back to a walk. This will help for several reasons, first it will give you control over his engine (his hind end) and secondly it will keep him soft and breathing. When horses get tight they hold their breath, if you can bend his rib cage and move his hind feet I think you can build up enough communication to get through this tricky time. It sounds like you have a lot of other things that are going well for you, try this out and let me know how it goes.
Best Wishes,
Caitlin Day Huntress