It wasn't on for more than 10 seconds. I watched it again this morning. If I were to guess:
It was right after we took the too many men penalty on the PP.
Stafford was the one that LR sent to the box for it. (I know it doesn't mean it was actually him committing the foul)
Once he got back from the penalty box was when LR started 'yelling' at him. Not sure if you could call it yelling, the crowd was celebrating a goal by the Flyers so it was pretty loud in there.
Stafford's words were "I know, I know".
I assume he was getting the talking to about getting on the ice too soon or not waiting for his guy or not realizing who he was replacing on the ice.
Then again LR could have been saying "You're a worthless piece of ###### Drew! You know the scouts are here tonight!" Staff: "I know, I know".