Here is why I think that it had to be a yellow. It was a line break and close to the try line. Barrett interfered with the play. If that was deemed to be on purpose then we wouldn't be having the discussion about the yellow. People think that it shouldn't be a yellow because he didn't do it on purpose. In other words, because it was accidental. There was a pretty good chance that without the interference, there would have been a try to the Lions. You can't change the penalty based on that because players will start feigning innocence going forward. A person accidentally trips into the opposing player. Take a look at what is happening with the latest rulings on hits to the head. If you make contact with someone's head then the player is off the field (either red or yellow), regardless of whether it's accidental or on purpose.
Aside from that, if you look at the replay you can see that Barrett was looking at his legs when he pulled away so he had to have seen the ball.
Just to add. Barrett has gotten 2 yellow cards for similar things during the season. Line break, committing a professional foul. He sort of loses the benefit of the doubt when that's the case.
