Here is commenter wavesinair’s report on (yesterday’s?) practice, 
cut/pasted in full:
Here’s what happened…
Richardson, who Murray calls “Richie,” was the offensive player and carried the puck behind the goal with Purcell on his tail.
As Richardson passed the goal and was nearing the corner he cut and went back behind the net in the other direction, again with Purcell in chase.
Murray immediately stops play and raises his voice. (The one thing about practice is there is very little yelling and very soft whistles.) So when Murray raises his voice, it’s noticed immediately.
Murray skates over and starts to lay into Teddy about how, as the defensive player, you cannot allow the puck carrier to turn around and go back behind the net. You must cut him off with body position and force him into the corner. (I liken this to basketball when you cut off the baseline as the defender.) Murray transitioned into talking to the whole group about the idea, not just Purcell, but at first the light was pretty much on him.
The operative phrase Murray kept repeating during this lesson was, “No Turn-backs!”