My first instinct is that he's only been with you for a short time. Most horses paw because they are anxious, afraid, angry, impatient... My guess is he is reacting to his move and not having his place yet. Horses are very ruled by rhythm and he's lost his. New home. New friends. Was he turned out 24/7 at his previous home? Was he in with lots of younger buddies to wrestle with? Was he eating at free choice there and now waiting for meals? Did the previous owners feed at 8AM and 8PM where as you feed at a different time in a different way? Any one of these things can make him anxious, afraid, angry, impatient etc... Perhaps he was near the top of the pecking order before and now he's at the bottom, this aggravates him. It could be anything.
I would however turn the lad out 24/7 so A. He can excersize and B. You can sleep. I'd give him a buddy, too.
I would NOT hobble this horse!
Secondly, if he is getting two kitchen cups of feed as indicated, I wouldn't bother switching his feed as two cups isn't enough to fill his left ear and is very doubtedly causing him to re-act.
Since you KNOW that OBVIOUSLY he is upset for some reason, hence the pawing, and you continue to work with him (lead him) I'd say the two are linked and he is not a vicious animal by nature, no horse is, every horse "wants" to be good. This is not an excuse, just all the more reason for you to look into WHY he is upset in the first place. If he stands around pawing its almost a no brainer to me that he'd rear at you on the lead, he's all keyed up.
Try to keep his rutiene as simple as possible, like I said, I'd leave him outside with someone who will play with him. I would also offer him free choice hay, just something to do all the time - EAT. If you plan to groom him daily, do so at the same time every day. So he knows "At 9AM mom feeds the other horses and turns them out. At 9:30 mom fills water tanks. At 10:15 mom brushes me." Keep it short and sweet. I am only suggesting this to help him settle in, not as a life long agenda.
However, he does have to know situation be d*mned he cannot attack people and I would be having a serious talking to with him on the lead rope right then and there when he does it, not fifteen minutes later in the round pen.