I have a little theory that all horses have a private leg - just one that is less easy to handle than all the others. Moreover, in male horses it is more likely to be a front leg than a back one. I believe that this is their "colt leg", the leg that took a lead role in colt games while the horse was young. The shoulder on that side is more likely to go into-pressure when touched or pushed and the horse is more inclined to nip the owner's back and to dip the leg or to strike out on that side. There is no reason to believe that horses can generalise and that they know that their legs come in a set of four! Here is Freddie who definitely exhibits this behaviour. With a lot of repetition he got a lot better today and by the end was happy to have this leg picked up whether headcollared or loose.