Smith has been scratched more than enough time. Quinn is a pretty good communicator. He has clearly communicated with is expected and what is non-negotiable. Apparently somewhere within there, DeAngelo has either a) not done what Quinn communicated to him he needs to do or b) tried to negotiate the non-negotiable.
I would doubt that.
I think that anyone who does not listen to what is demanded of them , finds themselves scratched. Clearly DeAngelo either understood and choose to do his thing anyway or did not listen when the lesson was being taught.
Quinn is building a culture. Part of that culture is what he communicates to the players about what they need to do and they way they need to play. If ADA has decided at times this season that those rules do not apply to him, Quinn has to show that he holds people accountable. Building a culture on a team like this is pretty important. Or rebuilding, that is.