So essentially, any player in a ruck or maul is putting another player at risk if they lift their foot off the ground and put it back down again? If thats true, then we should ban everyone who does it, and if its not true, than your logic for horwill knowing that someone was under him lies in tatters.
As for the Farrel incident, that is just as obvious, he has a clear line of sight of the player on the ground, and more damage was done. It is in almost every way, as bad as or worse than the Horwill incident. I am not, however, too upset about the whole incident not being reported, as i would much rather watch the bloke on the field, than see him off it surrounded by lawyers.