It's the same as every other aspect of the game. The refs have caused the problem, they need to make calls and blow penalties.
In their pursuit of allowing the game to "flow" there are several indiscretions every set of 6 which they let go. The one that bothers me the most is when they tell a player they were given a chance the first time, but this time it's a penalty. It's either a penalty both times or not at all.
Offside, not square at marker, not playing the ball on the mark, forward passes, those playing the ball interfering with the markers, players holding on too long, particularly when their defensive line isn't set. It isn't the refs job to decide on the extent of impact, While grey areas will always exist in the ruck, illegal plays must be penalised.
BJ was clearly looking at and obstructing Barba and should have been penalised regardless of the impact.