OP, what is your experience, exactly? Are you currently working with a trainer, and does that trainer have experience bringing horses off the track?
As I hinted above and as others have also hinted, if you’re a novice, it’s not advisable that you go and get an OTTB straight off the track. I’ve seen some exceptionally quiet horses at the track (I rode one bareback in a halter around the shedrow), but that doesn’t mean they’re necessarily suitable as a novice mount, because green horse/green rider is usually a very bad combination. Again, if you’re really itching for an OTTB, but you lack experience, try looking for one that has been off the track and already has mileage in the discipline of your choice.
If you are experienced riding green horses and/or do have a trainer with experience working with horses right off the track, then that option might be one to explore. But unless you offer more insight into your experience level, it’s hard to give really on-point advice here.
