Actually that's the criteria for getting disqualified. If your opponent makes an action first and makes contact with his upper body, then you're allowed to do it
i believe this is also allowed if YOU start the throw, but you must got him on your back before you grab his leg (btw you can do this without a leg grab..... actually in the original technique you don't let go of any of both sleeves....) regards
grabbing the pants hasnt always been against the rules you know.. some of the footage is probably old. But the arm is allowed to grab around the leg. not the pants, the leg.