doubt it! Rapping is the raising of a pole by hand/pulley to hit the horse as it jumps the fence. Banned under all BSJA etc rules but without question happens at yards. Within rapping you also get the use of objects within boots and glass/nails/wire (anything painful) along the poles to make the horse never want to hit a pole again! Its all to try make a careless horse careful. Very hotly debated from year dot and will continue to be so into the future. Don't approve of the methods at all but I know several showjumpers who do and will continue to use them to varying degrees.....
It is awful and as I recenly found out that its been done to my horse in the past Id like to find out more about it. My boy boy is petrified when he hits a pole.
sounds very probably then. there is one rider I know who raps in one way or antoher all their horses, They go off their heads if they touch a pole. There are other ways to make horses more careful and making them petrified is not one of them. All you can do is have patience and sit as quietly as possible on the occasions he knocks a pole, then hopefully slowly he will realise he won't get a beating.
Also if possible use lighter poles at first and possibly jump on the lunge.
Due to the fact rapping is banned I doubt very much if you will find a webpage on it. As mentioned it does still go on but those who do it will not be found talking openly about the fact!
IMO it does not make a careless horse more careful, just puts the fear of god into them and causes more problems than it solves. Fact of life is some horses are naturally more careful than others, just like some humans are more clumsy that others.
It sounds like your horse has been rapped and as you find this upsetting enough I would advise against digging any deeper as it could really distress you. Some of the practises used can be exceptionally unpleasant.
Good luck in helping your horse overcome his man made problem, with patience and care you will get there.