I see this WAY too often in my travels. A person has a horse that is troubled while being led and the person has their forearm against the horse’s neck shoulder in a vain attempt to keep the animal off of them.
Simple biological fact: most horses weigh about FIVE TIMES what we do Their core instincts are to push against another being for either dominance, security or evasion. Why in the world would a puny human think that by putting their arm against the horse’s neck/shoulder, they can keep that animal off of them???
I have seen this attempt at control from all level of horsemanship. From uneducated local level beginner rider/handlers up through Olympic caliber trainers. The most common thread I have heard was “if you keep the lead line short and your arm stiff, you can keep them off you”. No, they just learn to shove you out of the way.
There is physiological changes in a horse that crops up from this type of handling. I have had horses come in for training that have never been ridden that have over development of the left shoulder from being braced up against the human.
Groundwork, it’s not just for breakfast anymore . . . . .