1. Ridleys first reaction was that it was a knock on only as the Bath player made a genuine effort to catch/intercept the ball. Therefore scrum to Sale
2. TMO urged him to have a 2nd look which he did. He then decided that it wasn't a genuine attempt to intercept because 'he didn't use both hands'. Hence deliberate knock on- Sale penalty.
3. His rationale for no yc was because it did not deny Sale a try scoring opportunity
I agree that a 'deliberate' knock on should be penalised. But I think we should be more aware of what is a clear, cynical, deliberate attempt to illegally prevent a pass and what is a genuine attempt to intercept the ball. As such, I am not sure that the decision of deliberate knock on is always right. It is all down to perception and yesterday's incident could probably been argued both ways.
I don't agree with Ridleys assertion that it must have been deliberate because he only got one hand on the ball. How many times do we see a good interception where the players initial touch is only with one hand? To be fair to Ridley, he did also say that if the player attempts an intercept, he is taking a risk of being penalised if it goes wrong. Also there have been plenty of occasions where a yc has been shown for a deliberate ko, where the attacking team have not been deprived of a clear try scoring opportunity.
I don't pretend to be as aware of the finer details of the laws as Ridley presumably is, but I did find some of his rationale over ref link at the time to be slightly odd.