From an article in The Telegraph about the Farrell ban:
In his evidence, Farrell explained that he believed the tackle had been through the chest area and a fair tackle, and that it would have felt different had he put the force through the chin. Once Farrell returned to the team bus and reviewed clips of the incident, he realised contact was made with the chin and contacted Clement to apologise.
The panel determined that "the contact with the head or chin was not intentional but instead reckless", while adding: "The panel accepts the player believed he had primarily struck his opponents chest. The footage, in our view, demonstrates he was wrong.
Looking at the clip, he didn’t even bother to look where he was aiming at. Nor attempts to wrap either hand. So even if he had of hit the chest area, which he conveniently claims to have done, he hasn't wrapped so it isn't a legal attempt to tackle. So how it can be argued that he thought it was a fair tackle seems nuts...