I realize that if an iron golem is ever moved by a lead, after the release its motion become very sluggish. For example, if I used a lead to move a golem and then release it, beating it at this point he will struggle to move to the player to hit the player.  If I try to get close at this point he can hit me normally, but if I walk off again I can see it tries to move but it fails.

Similar behaviours seem to occur to other animals like cats, which is less likely to escape from the player once they were attached to a lead and released.